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f ■ t

TEXT BOOK

FORTIFICATION AND MILITARY
ENGINEERING,

FOB USE AT

THE EOTAL MILITARY ACADEMY, WOOLWICH,

LONDON:
Printed ytidar the Superintendence efHer Majettg'e Slalianerg Office,

W. Cu>w)ss & Sons, 18, Charing Cross ; Harbiboh & Soks, S9, Fall Mall ;

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LONOKAM & Co., Paternoster Bow ; Tuvbst.h & Co., 57 & S9, Ludgate Hill;

Stanfobd, Charing Crofis i H. S. Kiso & Co., 65, Comhill .

Alio by GiUETiN & Co., The Hard, Portsea ;

A. & C. Click, Edlttburgh;

AtMX, Tho«. Abbey Street, and E, Ponbomby, Grafton Street, Dublin.

1877.

Price Thirteen SMlHnga and Sixpence.

PREFACE.

This Text-book is intended to assist the cadets of the Royal
Military Academy in the course of fortification laid down for
them. It has, therefore, been adapted to that course, of which
the leading principle is, that in so far as it is obligatory, it should
not be carried beyond the point useful alike to officers of the
Boy al Artillery and of the Boyal Engineers. All unnecessary
detail has been avoided, and much in the way of explanation and
illustration is left to be supplied verbally during the course.

To make the book, however, complete and independent so far
as it goes, in the present edition all the figures referred to have
been lithographed and bound up with the text.

Geometrical drawing and projection are treated of only as
preparatory to fortification, and to the extent required for under-
standing and making fortification drawings* An outline of
geometrical perspective has been included, as that kind of pro*
jection is in some cases the most suitable.

The chapters on fortification have in earlier editions been
preceded by a short account of the arms in use. But artillery
material has now become so complicated and various that it cannot
be made intelligible in a few pages of description. The reader is,
therefore, referred to other works, such as the Handbook for
Field Service, or the Text-books of the several departments of the
Royal Arsenal, for information as to the nature of arms and
ammunition; their effect upon works of defence is noticed as
occasion arises.

The ** Instruction in Military Engineering," prepared at Chat-
ham, has been followed in all parts of this book dealing with the
subjects to which it relates, in accordance with the order issued

by H.B.H. the Field Marshal Commanding-in-Chief.

The i:ecent changes in permanent fortification have lessened the

importance of the study of the older systems. The time seems to

have come, therefore, to depart from the historical order, and to
4g642, m7302, ^ 8

direct attention first and mainly, to modern principles of construc-
tion* Those who have mastered these can afterwards study the
development of fortification^ and the various historical systems^ of
which some notice will be found in Part 2. Others will have an
opportunity of gathering from lectures some idea of this develop-
ment.

Part 2 will also contain chapters on the attack and defence of
fortresses^ the execution of siege and field works^ mining, coast
def enceSj and military bridges.

Eeferences are in many cases made in footnotes to works from
which the reader may obtain fuller information on particular
points. It is hardly possible in a book of this kind to make all
due acknowledgments, but the frequent assistance derived from
the works of Captain Wagner^ Captain Brunner^ and General
Brialmont^ should at all events be mentioned.

I >i • •

TABLE OP CONTENTS.

CHAPTER I.

GXOMETBICAL DOAWIMG.

Section 1.— Practical Plane Geometry :—

Use of instruments

Problems in practical plane geometry
Section 2.— Practical Solid Geometry : —

Principles of projection

Projection of geometrical solids

Elementary problems in solid geometry

Further problems in solid geometry

Isometric projection

Perspective projection

Defilade problems • - -

Paoii

1
5

15
20
23
26
32
34
43

CHAPTER n.
Elementabt Field Fobtificatiok.

Section 1. — Introductory: —
Objects of fortification
Ranges and effects of firearms
Section 2. — Clearing the ground
Section 3. — Hasty Intrenchments :—
Shelter trenches

•

46
47
49

Gnnpits^ ...
Section 4, — Obstacles: —

. a 1

Abatis, entanglementSi &c*
Fougasses - • -
Inundations

• • 1

55
59
60

Section 6. — Adaptation of Accidents of the Surface:**

Hedges ----.-•
Walls

61
61

Embankments and cuttings
Section ^.— Field Works :—

. • •

Profile ...

•

« • •

Trace of works

M • •

Sixe and garrison of works -

• . i

■ 73

VIU

Faojc

Section 4.— -Fortresses and Forts :—

Origin of fortresses

- 179

Yauban's frontier lines

m m

- 179

Opinions on the use of fortresses

since 1815

- 180

Experience of the last war

m m

. 183

Classification of fortresses -

. 184

Outworks and advanced works

•

- 184

Detached works

- 185

Increased use of detached works

- 185

The fortress of Antwerp -

- 187

Details of detached forts •

- 188

Keeps and citadels -

» m

- 191

Provisional fortification

■

- 192

Appendix A.-
Appbndix B.-
Appendix C-
Appendix D.-

-Table of linear measures
^Table of B Jti.L. ordnance
-Blockade of Metz
-Assault of the Duppel position

193
195
196

198

TEXT BOOK

FORTIFICATION AND MILITARY

ENGINEERING.

CHAPTER I.

GEOMETBICAL BBAWINO*

Section 1. — Practical Plane Geometry.

1. Before any advance can be made in the study of fortification^
it is necessary to acquire some knowledge of geometrical drawing
and of the principles on which the drawings required to represent
works and buildings accurately are constructed.

The instruments used in geometrical drawing and the mode of Dnwing
using them will first be described.* iiwtnuiieiiu.

Compasses for drawing circles are provided with a moveable leg CompMses.
to admit of a pen or pencil leg being substituted for it Com-
passes intended merely for measurement are called dividers.
When the compasses are in use they should be held at the top^
between the forefinger and thumbs with one or more of the other
fingers under the hin^e, to increase or diminish the distance
between the points gradually or without a jerk ; and, in all cases,
the steel point should be guided by the finger of the other hand to
the centre ki£ the circle to be drawn, or to the line or scale to be
measured. When several concentric circles are to be drawn, great
care is requisite to avoid enlarging the centre hole, for which
purpose diuughtsmen lay a small piece of horn, card, or other
similar material under the point.

In taking off distances with the compasses, they should be
opened wider than the required distance, and closed to it. In
describing circles with the large compass, the pen 1^ should be
bent at the joint so as to be perpendicular to the paper.

* These instractiooa were originaUy drawn np for mere beginnen, and will be
nnneeessaTYfor those who are already familiar with the elements of geometrical
drawing. The practical hints in them may, however, be of nse to a&y who find
diffictdty in working with their instrmnents.

OEOMETBIGAL^DBAWIKG.

Bow-sweeps.

Drawing pen.

Protractor.

Sector.

2. Two pairs of small compasses^ one with a pen leg, the other
with a pencil leg, are used for drawing smaller circles than can be
conveniently described with the larger compasses. These small
compasses are called boto-sweeps. They should never be used for
drawing arcs of above l^-inch radius.

3. The drawing pen is used for drawing straight lines, thick or
thin, according as the nibs are set more or less open.

It should be held close against the ruler, and slightly inclined
in the direction of the line to be drawn. Be very careful to make
both nibs touch the paper, and to preserve an even pressure, and
the satne position of the pen with regard to the paper and ruler
throughout ; by which means an equal thickness will be secured
and ragged edges avoided. The pen should be always put away
clean and dry, or it will soon become clogged with old ink and
rust, and be unfit for use.

4. ThQ protractor is an ivory scale, of which the chief use is to
lay off, or protract angles by means of the radiated lines on its
edge. It has also marked on it various useful scales.

The protractor should not be used for setting off angles, the
lines containing which are required to be accurate for a greater
length than^^lj or 2 inches.

The scale of chords, marked C H O, affords a more accurate
method of setting off an angle. Using the distance from zero to 60°
on this scale as a radius, describe an a,rc, and set off as a chord of
this arc the distance from zero to the division corresponding to
any given angle, this chord will subtend the given angle at the
centre from which the arc is described.

The protractor has also usually a diagonal scalcy sometimes
half-inches divided into hundredths, with quarter-inches at the
other end, or, which is a much more useful scale, inches divided
into hundredths. To take off a given distance, say 4*35 units,
look along the horizontal line marked 5 (for 5 hundredths), place
one point of the compass on the point where this horizontal line
cuts the fblique line from the point 3 (for 3 tenths),'and the other
point of the compass where the line is intersected by the perpendi-
cular from the point marked 4 (for 4 units).

5* The sector is an instrument formed of two flat arms or rulers,
of equal length, connected by a stiff joint, and moveable about its
centre in a plane.

The principal uses of the sector are,- —

• To divide given lines into any number of equal parts.

To find a required fractional part of a given line.

To find 3rd or 4th proportionals to given lines or numbers.

To s6t off angles of given magnitudes.

To divide the circumferences of circles into equal parts for
the purpose of describing regular polygons, or to find the
radii of circles circumscribing polygons of given sides.

The scales for the above purposes are on one side of the sector;^
which also has a useful scale of inches and tenths.

PBACTIOAL PLANB GEOMETBT. 3

The scales on the other side are not so generally required,
referring mostlj to navigation, &e.
To use the sector*: —

Ex. 1. To divide a line into 9 equal parts. U<e of ^ line of

Open the sector till the given line to be divided is the transversa Unesy" L L.
distance between 9 and 9 on the respective arms of the lines
marked LL (called the line of lines), then the transverse distance
from 1 to 1 will be -J^th of the given line^ 2 to 2 will be f ths« and so
on.

Ex. 2. If a fractional part of a line be required, and the denomi-
nator of the fraction is greater than 10, the seoondaiy divisions of
the line of lines must be used, and in order to bring the resulting
line as far from the centre (of hinge) as possible, for greater
accuracy, multiply the numerator ana denommator of the fraction
by some numbcar which will not bring the denominator above 100,
the number of secondary divisions in the line of lines.

To find ^ of a given line, ^ = fj, set off the given line as a
transverse at 84, on the line of lines, then the transverse at 20
will be the reauired fractional part of the given line.

Ex. 3. To aetermine a 4th proportional to 3 ^ven lines.

Let A, B, C stand for the lengths of the given lines, and first
suppose A the greater of the two, A and B. The length of the
line A being taken in the compasses, set one of its points in the
division 10 of the line of lines on the sector, and open the instru-
ment till the other point falls into 10 of the other limb : then,
taking the line B in the dividers, find what two divisions, or
subdivisions, having the same number, this distance subtends on
the sector. Let p stand for this number ; then setting the length
of the line C between 10 and 10, the distance between the numbers
p p will be the fourth proportional required.

If B were greater than A, then B must be set between 10 and
10, and let q stand for the length of A determined as p was
determined in the former case ; then C being set from q to q, the
distance from 10 to 10 will be the fourth proportional.

Ex. 4. To find a 4th proportional to two numbers, a and b, and
a line C.

Make the line C the transverse distance between the divisions
corresponding to a, then the transverse distance between those
corresponding to b will be the required 4th proportional. If a and b
were numbers greater than 10, say 21 and 47, then the seoondarv
divisions must be used, multiplying in this case both numbers by 2,
in order to bring the construction as far as possible from the hinge
of the instrument.

Ex. 5. To set off angles of given magnitude with the sector. Use of'Mineof
the line of chords marked C C is used. Take the radius of any chords/' C C.
arc, and open the sector till this radius becomes the transverse
distance from C to C, then the chord of this arc for any required
number of degrees will be found as the transverse distance between
the corresponding divisions on the line of chords.

It is evident that an angle of a given number of degrees may be
readily divided into a number of equal parts by means of the line
of chords.

Ex. 6. To describe a regular polygon of n, sides upon a given Line of poly-
line, open the sector till the transverse distance between the gons.
divisions corresponding to n on the line marked POL is equal to POL.|
the given side, then the transverse between 6 and ^ will be the
radius of the circle circumscribing the required polygon.

"** In all cases when measuring transverse distances, tjiat is, distances measured
from a point in one line of a pair to the corresponding point in the other line, the
points of the dividers must be applied to the divisions on the innermost lines in each .
case, that is, to those which radiate from the centre; the extremities of these lin^s
are usually marked with brass points.

4 GEOUETSICAL DBAWIKO.

Marquois 6. Marquois scales consist of a right angled triangle} of

^^^ boxwood or Yulcanite^ of which the hypoihenuse is (usually)

three times the length of the shortest side^ and two rulers. Each
ruler has along its edge two scales, the outer termed the artificial^
and the inner the natural scale. Each inner or natural scale is a
simply divided scale of equal parts of an inch (20ths, SOths, &c.)}
numbered from left to right, the first primary division being
divided into ten of these equal parts. The divisions of the outer
or artificial scale are equal to three times the length of the equal
parts on the inner, so as to have the same proportion to them that
the longest side of the triangle has to the shortest, and these
divisions are numbered each way from the central zero point, 0.
The triangle has an index or pointer in the centre of its longest
side.

These scales are very convenient for drawing parallel lines at
given distances apart, and are therefore most useful in fortification
drawings of small size.

' Ex. — To draw a parallel line at a distance of ^ of an inch firom
a given line, place the triangle with its bevelled edge coinciding
with the given line. Set the ruler with the scale marked 20 closely
against the hypothenuse and the zero, or any other division of the
artifidal scale corresponding with the pointer. Slide the triangle
along the rule r to the right or left as required, till the pointer
corresponds with the 7th division from the starting point or zero.
The line drawn along the bevelled edge of the triangle in its new
position will be the line required.

One of the advantages of the Marquois scales is that the sight
is assisted by the divisions on the artificial scale being larger than
those of the natural scale to which the drawing is constructed,
and any error in setting the pointer produces an error of but one
half or one third the amount in the drawing. Their defect ,is
that, except in the case of very small drawings, they have often
to be shifted, and in so shifting them errors may readily creep in.

General rulei. ?• The following problems comprise only those of which a know-
ledge is essential before beginning the study of projections and
fortification. Many of them are used in tracing on the ground
the outlines of works of defence, and should be clearly impressed
on the mind.

Before proceeding to the problems, the following general rules,
applicable to all geometrical constructions, are given, as being of

Sreat use in ensuring accuracy and avoiding waste of time and
hour.

1. — Lines should be drawn long enough at first to avoid having
to produce them. A long line should never be obtained by pro-
longing a short one ; unless, in the case of a straight line, a distant
point in the prolongation has been first found by other means.

2. — ^Whenever it is practicable, lines should be drawn /rom a
given point, and not to it ; and if there are several points, in one
of which two or more lines meet, the lines should be drawn from
that one.

3, — The larger the scale of a geometrical construction, the less

CD. PL I

Fi^.2,

D B

Fig. 3.

B B^^

^yp A

Fi^ i.

C --- - " i) B

tr Fig. J.

Fig A).

A i:

\ \
" I

O Jt) B

Opp.to-pax^^i .

Dangerfiela Litl; 22. Bedford S^ Crvent '".Uixlen

PBAOnOAL PLANS OBOMBTRT. S

the liability to enor. Hence, angles should be set off^ and pobts
determmed, by means of the largest possible circles.

4. — In determining a point by the intersection of dronlar arcs
or straight lines, they should meet at an angle as near 90^ as
possible, and nerer at a less angle than 20^.

5. — ^When one arc or straight line intersects another as above,
the intersecting point (mly of the sec<md need be marked, as it is
desirable to avoid unnecessary lines.

6. — Never set off equal lengths on a given straight line by
continual repetition of one such length, but mark off, on the line^
a convenient multiple of the given length, and subdivide it This
is especially applicable to the construction of scales.

Problems in Practieal Plane Geometry*

8. To bisect a given angle. FaoBuic i.

Let BAG (Fig. 1., PL 1) be the angle; in AB, AC, make
AE equal to AD ; then with D and E as centres, and with equal
radii describe arcs intersecting in F. Join AF : it bisects the
angle BAG.

To bisect an angle traced on the ground by pickets or other
marks, as BAG, u a mark at any point E in AB, as far from A
as possible, and another D at an equal distance from A in AG.
Double a cord, so as to find its centre, and fixing its two ends at
E and D, stretch it by its centre, which will mark a pcnnt eqtu-
distant from both. The line bisecting the angle will pass through
this point.

8. Through a given point to draw a line perpendicular to a Pbobum s.
given line.

(1.) When the point P (Fie. 2) is in the given Hue AB, and not
near either end, set off equal distances PG, PD, in AB. From C
and D as centres with any radius describe arcs intersecting in E,
join PE, which will be the perpendicular required.

(2.) When the point P (Fig. 3) is in the line AB, but very
near one end of it, take any point G without the line as centre,
and with radius GP describe an arc, cutting AB in D. Join DG,
and produce it to cut the arc again in R Join EP: the angle
EPD, being the angle in a semicude, is a right angle.

Or, take any scale of equal parts, and set off from P, along the
line AB, three of these equal parts to G. Then with P as centre
and a radius of four parts, and G as centre with a radius of five
parts, describe arcs intei^ecting in the pmnt D. PD is the per-
pendicular required — the square of five being equal to the sum
of the squares of three and of four. This construction may be
advantageously used on the ground.

(3.) When the point P is not in AB. From P (Fig. 4) as
centre with any convenient' radius, describe an arc, cutting
AB in G and D. From G and D as centres, with any radius,
describe arcs intersecting in £ on the opposite ride (^ AB. PE
is the perpendicular required,

GEOMETBIOAL DE^WINO.

Fboblem 3.

Problem 4.

Problem 5.

Problem 6.

(4.) When F (Fig. 6) is nearly opposite tiie end of AB» draw
PC at any convenient angle to AB, G beine a point in the line
AB. Bisect PC in D, and describe a semicircle on it^ cutting
AB in £. P£ will be the perpendicular required.

10. Through a given point to draw a line parallel to a given
line.

Let AB (Fig. 6) be the given line and P the ^ven point.
From P draw PO perpendicular to AB. Take any point ia the
farther end of the line. A, as centre^ and describe an arc with
radius equal to the perpendicular PO. Through P draw a line
touching thisarc ; it will be parallel to AB.

Or^ take any point A. in AB, as far as possible from P. From
A as centre^ with radius AP describe an arc cutting AB in D.
And with D or P, as centre with the same radius, another arc,
cutting AB in A. Make the chord AE equal to the chord PD,
and upon the same side of AB. The line PE will be parallel
to AB. This is the most convenient construction for employment
on the ground.

11. Through a given point to draw a line which will pass
through the point in which two given lines, if produced, would
meet.

Let P (Fig. 7) be the given point, situated between the ^ven
lines AB and CD.

Draw through P any line, cutting AB and CD ^in E and F ;
and at any convenient distance from EF another, parallel, cutting
AB and CD in G and H. Job the diagonal ER Through P
draw a line parallel to CD, meeting the diagonal in L, and
through L a fine parallel to AB, meeting GH in Q. The line
joining P and Q will, if produced, pass through the point of meeting
of AB and CD, for by similar triangles EP : PF : : GQ : QH.

If the point P is outiside the given Unes, and nearest to the
line AB (Fig. 8), drawing the parallel lines as above, join PH.
Through E draw a line parallel to CD, meeting PH in L. And
through P a line parallel to the line joining L and G and meeting
the line GH produced in Q. Then EF : EP : : GH : GQ.

12. To construct an angle of a given magitude.

Let DCE (Fig. 1, PI. 2) be the given angle, and A. (Fig. 2)
the point in the given line AB at which it is required to construct
an angle equal to the angle DCE. With centre C, and any
radius CD, cut the lines forming the angle in D and E.
And with centre A and the same radius describe an arc, cutting
AB in B. Make the chord BF equal to the chord D£. Join
AF : it will make the required angle with AB. The scale of
chords on the ivory protractor, or the line, of chords on the sector,
may be used for setting off angles of a given number of degrees.
(See paragraphs 4 and 5.)

On the ground, angles are most readUy set off by a theodolite
or sextant, or by a table of natural tangents.

13. To construct on a given line a rectilinear figure similar to
a given rectilinear figure,

0.0. PL. 2

Fig«. 1.2

Fig. 5

X '

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Fi^.r

(}Tffi:t4 ,-^»(L<ie7.

Figs.3 . 4.

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1 1

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*> ^^.^ "... "^^ --'

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PBAOTIOAL PliANB OEOWBTRX. 7

Let a b (Fig. 3.) be the given Ime, and ABCD^ &o. the given
figure. Taking the side AS (Fig. 4) as homologons to the side
a b, set off Ai' equal to a A along the line AB, produced if
necessary. Join AC> AD^ &c. the angles of the figure ABCD, &c.
Through V draw b' d parallel to the sides BC> 'cutting AC| or
AC produced^ in c'. Through c* draw d H parallel to CD, and
so on in order. At the extremity of the given line a A, make a
series of angles with a b equal to the angles BAC, BAD, &a,
and set off on these lines the distances A c', A d\ &c* in order.
Joining the points, a figure similar to Afi, CD, &c. will be
described on a b.

14. To divide a given straight line into any number of equal Pkobluc 7.
parts.

1. When the number (n) into which the line is to be dMded
is not greater than 20.

Open the dividers to what appears to be the rfi^ part of the
line. Set off successively this distance along the line from one
end to the other, and if it be found either to exceed or fall short
of the nth paj.t, correct the opening, and repeat the trial till the
exact n^^ part is obtained.

If n can be resolved into two factors (p and y), one of which,
j7, is any power of 2, as 4, 8, &c. ; the line should be first bisected
(which can always be done by two trials). Each part should be
again bisected, and so on tUl the line is divided into p parts.
Each of these may again be divided into q parts, the q^ part of
one being obtained by trial as above.

For example, let it be required to divide the line into 12 parts.
First bisect the line, then bisect each half again, and lastlv divide
each 4*^ part into 3 by trial. Or divide the whole line by trial,
first into three parts, and then bisect each third part twice in
succession.

If the line is to be divided into 10 parts. First divide it by
trial into five, and then bisect each division. Or, first bisect the
original line, and then dividing it into five parts by trial, set off
the ^*^ part twice from each extremity, and twice each way from
1^Q middle point of the line.

In bisecting a line it is well to open the dividers as nearly as
can be guessed to half its length. Then, setting off this length
from each end of the line, bisect the small distance between the
two points marked, by the eye, with a sharp pencil or the pmnts
of the dividers.

In all these trial divisions, care must be taken not to mark the
paper with the points of the compasses till the correct distance
is found. By sector.

The sector may be used for dividing a line into a number of
equal parts, or obtaining a required fractional part of a given line.

15. A given line may also be divided by the following con- By geometrical
stniction (Fig. 6) : From one of its extremities draw a line making coostrnction.
any. angle (not less than about 30) with the given line. Set off

with tKe dividers along this Hne thus drawn the ^ven number of any

OBOMEtBlOAli BBAWlKa,

Fkoblbm 8.

equal parts. Job the extremity of the last divkion with tiie
other end of fhe given line, and draw parallelfl to this third line
through the points of division. These parallels will divide the
given line into the required number of equal parts.

16. To draw parallel lines at given distances apart through
the points of division of an equally divided line.

Let A B (Fig. 6)3 be the given line divided into n equal parts.
From the centre B, with radius equal to n times the given
distance at which the required lines are to be apart, describe an
arc, and from the extremity A draw a tangent to this arc. The
required lines will be parallel to this tangent through the points
of division of A B.

Problems. 17t To draw the circumference of a circle passing through

three given points —

(1.) When the centre is accessible. Join any two of the given
points with the third (Fig. 7). Bisect these lines by perpendicu*
lars. The centre of tiie circle will be in the intersection of these
perpendiculars.

(2.) If the centre &lls without the limits of the drawing, the
circumference may be determined by a succession of points, by
the following construction.

Let A, B, and C (Fig. 8) be the given points. Join A and C,
the two ftirthest apart. The angle ABC will be the angle in the
segment of the required circle on the line AC. From A and C as
centres, with the same radius, AC, describe arcs : produce AB
and CB through B to meet these arcs in D and E respectively.
From D towards C on the arc set off any equal parts, 1, 2, 3, &c. ;
and on the arc through E set off the same equal parts, 1', 2\ 3',
&c. but outwardly from the point E. Join Al, A2, &c. and Cl',
C2', &c. The points in which these lines drawn to the similarly
numbered divisions on the arcs intersect will be points in the
required circumference. For the angle DAI is equal to the
angle ECl^, being angles subtending equal arcs in equal circles,
therefore the sum of the angles CAl and ACl' is equal to the
sum of the angles CAB and ACB, and therefore the angle at the
intersection of Al and Cl^ is equal to the angle ABC, hen(3b
this intersection is a point in the required circun^ference.

Problem 10. 18. To draw a segment of a circle on a given straight line to

contain a given angle.

Let AB (I^. 1, PL 3) be the given line, and C the given
angle. At A miake the angle BAD equal to the given angle C.
From A draw AE perpendicular to AD. Bisect AB by a line
FH perpendicular to it, and meeting AE in H. With H as
centre, and radius HA=HB describe a segment on the line AB.
The angle in this segment equals the alternate angle BAD, and is
therefore equal to C.

Problem 11. 19. To draw tangents to given circles from points either in or

without the circumference.

(1.) Let P (Fi^. 2) be a point in the circumference of a given
drcle, of winch C is the centre. From F as centre with a radius

C.D.PL.3

Fig.l.

Fig 6.

Fig. 5.

Fig.l.

— t

'-^ :

-— J>

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I \
\ >
I \

0/ 1 — / \ — \P

TVfj

Opp: bo jKLCfp. •9.

j;->ii;'ft^tjdd Lii.^. ;'.. B'-dicrdS! i; jv-^nt CUrden

PRACTICAL PLANE GEOMETRY. 9

equal to PC describe an arc cutting the circumference in E.
Join C£ and produce it. From E as centre, with radius EC
describe a semicircle cutting CE produced in F. Join FP, this
will be the required tangent, the angle FPC being the angle in a
semicircle.

(2.) Let P (Fig. 3) be a point without the circumference.
Join PC and bisect it in E, and from E as centre with radius EC,
describe a circle on PC, cutting the circumference in F and O.
PF and PG will be tangents to the given circle.

20. To draw arcs of given radii tangential to given lines and PjioBunf is.
given circles —

(1.) Let AB (Fig. 4) be a given line, O the centre of a given
circle, and R the given radius of the required circle.

Draw a line CD parallel to AB at a distance from it equal to R.
From the centre O, with a radius equal to the radius of the given
circle + R, describe an arc cutting CD in E. The circle described
with the centre E and the given radius R, will touch the line AB
and the given circle.

(2.) To touch two given circles externally —

Let R (Fig. 5) be the radius of the required circle. From the
centres of the given circles, with radii equal in each case to that
of the given circle + R, describe intersecting arcs, the points of
the intersection will be centres of the required circles.

(3.) To touch one given circle externally, and to be touched
internally by the other given circle —

Let C (Fig. 6) be the centre of the circle to be included, and
D the centre of the other given circle. From centre C with a
radius equal to the difference between R, and the radius of circle
C, describe an arc. From D with a radius equal to that of D + R
describe an arc, the intersection of these will be the centre of the
required circle.

To include and touch a circle, the locus of the centre of the
tangential circle will be the arc described from the centre of the
former with radius R — rad. of circle ; to exclude and touch, R +
same radius.

The limits to the length of the given radius (R) in the above
cases are —

(1.) If the circle he without the given line, R cannot he less
than half the interval between the line and thQ circle.

(2.) R cannot be less than half the interval between the given
circles.

(3.) R cannot be less than half the diameter of the circle to be
included pius half the interval between the given circles.

When a circle and a straight line are to be drawn touching
each other^ the circle should be drawn in ink first, and the line
then drawn from the point of contact to meet or touch it. It is
difficult to draw a circle to touch a line, but easy to draw a line
to touch a circle : and whenever two circles are to be drawn to
touch each other, the point of contact should be determined by
joining their centres. In the former case also, the point of contact
should be marked by means of the radius perpendicular to the
tangent.

42642. n

GEOMETRICAL DBAWINO.

Problbm 13.

Pboblbm 14.

Fboblem 15.

JtTROBLBM 16.

21« To divide a given line in a given ratio, or Bimilarly to a
given divided line —

(1.) Let AB (Fig. 7) be the given line, to be divided in the
ratio o{ I : m : n.

Draw from one extremity A, of the ^ven line, a line AC,
making a convenient angle with it. Set off on AC from any scale
of equal parts divisions corresponding to /, m, n. Join the final
division n, with B, and draw parallels through m and /. These
parallels wUl divide the given line in the required ratio.

(2.) Similarly to a given divided line (Fig. 8) —

Let OP be the given line divided in the points /, m, n, &c,, and
AB the line to be divided. Place AB parallel to OP at any
convenient distance from it. Then join AG, BP, and produce
them to 'meet in Q. Draw lines from Q through Z, iw, «, &c.
They will divide the line AB similarly to the line OP.

22* To determine a fourth proportional to three given lines —
This may be done in the same manner as Prob. 13, or, with
the compasses only, by the following construction, which is useful
where a number of fourth proportionals have to be obtained with
reference to the same pair of antecedents.

Let A, B, and C (Fig, 1, PL 4) stand for the lengths of the
three given lines. Describe two concentric circles with A and B
as radii. Mark points in each circumference, P and Q. From P
set off on the circumference of the circle whose radius is A, the
length PR =C. From R with the distance PQ cut the other
circumference towards the same direction in S. The chord QS
will be the fourth proportional required ; for, subtending an equal
angle at the centre with the chord PR, it will be proportional to
the radii of the two circles — ^that is as A : B.

If C is greater than the sum^ or less than the di£Perence between
A and B^ these radii must be increased or diminished proportion-
atdy.

Ijhe fourth proportional can abo be obtained by means of the
sector (see par. 5).

23* To determine a'mean proportional to two given lines —

Let A and B (Fig. 2) be the given lines.

Draw an indefinite line, and set off on it the two given lines A
and B in succession, so that the whole line CD may be equal to
their sum. On this line describe a semicircle. And through the
point indicating the common extremity of the two given lines
draw a perpendicular to CD. The portion intercepted between
CD and the semicircle will be the mean proportional required.

24. To divide a straight line in extreme and mean ratio.
A line AB is said to be divided in extreme and mean ratio, or
medially in C, when, —

AB : AG:: AC : CB. (Fig. 3.)
From B, in the line AB, draw BD perpendicular to AB and
equal to half AB. Join AD. With centre D and radius DB
describe an arc cutting AD in E. Cut off from AB a part AC =
AE. C will be the point required.

C.D.PL.4

A
B
C

Fig.1.

Fig. 2.

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I/an^*vf;el.i.Lith 2 2. Bedford Sv Ccreni Garden.

PRACTICAL PLANE QEOMETBT. 11

Let the arc cut AD produced in K

Then AB : AK::AE : AB

.-.AB : AK — AB::AE : AB — AE

But AB=EK and AE=AC,

AK— AB=AC,

And AB— AE=BC,

/.AB : AC::AO rBC.

25. To determijie lines, which, with reference to a given line Vmowlmh 17,

as unity, may represent \/2, \/3, \/5, &c., or A/n A/o A/ 5

&c.

Draw two lines at right angles to one another and meeting
in A (Fig. 4). From A set off on both lines the given
linear unit to B and C. The hypothenuse BC will be equal
to \/2. Set off this length BC_from A to D on the line AB.

Join DC, which will be equal to \/3. Set off along the line AC the
length BC to F, and along AB the length DC to E. EF will

equal \^5y &c.

If the linear unit were the edge of a cube the lines \/2 and \^
would be respectively equal to the diagonal of a face and the
diagonal of the solid.

(2.) On the line representing the linear unit describe a semi-
circle, then the chord of half the semicircle will be equal to

If a semicircle be described on a line AB made equal to 4 of
the linear unit, and if from the extremity A, a segment equal to
the unit be set off along the diameter to C, then the line at right
angles to the diameter, through C, and terminated by the

drcumference, will be equal to a/ 5.

By the same proceeding the A/- ^^7 he found, only AB

must be made equal to .

26. To construct a regular polygon of any given number of Pbobudc 18.
sides on a given line.

The equilateral triangle and the square do not require any
description.

Pentagon. — Bisect the given side AB (fig. 5) in C. From
Cj draw a line at right angles to AB and make CD in this
line equal to AB. Join one of the extremities A, of the base,
with D, and produce AD making the part produced DE equal to
AC. AE will be the length of the diagonals of the pentagon.
From the centre A with radius AE cut the perpendicular from C,
in the point F, this will be one of the angles of the pentagon.
The remaining angles will be found by the intersection of arcs
with radii equal to the given side, AB, described from the centres
A, B, and F.

B ^

12 GEOMETRICAL DRAWING.

In a regular pentagon it will be seen that the diagonal is four
times the sine of 54o considering half the side as unity ; now sin
54o=i (\/ 5 -f 1) .*. the diagonal = v' «*>+ 1? an«l by the above
construction the diagonal was made of this length.

In a regular pentagon, if the length of the diagonal he given, the
side of the figure can he found by dividing the diagonal in extreme
and mean ratio. The greater segment will be the required side.

Hexagon. — Describe an equilateral triangle on the given side^
With the vertex as centre describe a circle ; it will circumscribe
the required hexagon.

Heptagon, &c. — The following is a general construction for all
polygons. (Fig. 6.)

Produce the given side in both directions. From the extremities
of the given side as centres with radii equal to the said side
describe semicircles on the line. Divide these arcs into (n) equal
parts and through the second division from the outer extremities
of the arcs draw lines to their respective centres. These lines
will make with, the given line the angle of a polygon of (n) sides,
thus forming three of the required i?ides. Bisect these sides by
perpendiculars, which will intersect in the centre of the circum-
scribing circle, and the remaining sides can be set off on it.

The sum of the interior angles of a polygon is equal to twice as
many right angles as the figure has sides less four right angles.
Therefore in a polygon of (n) sides these angles are equal to

2 w X 900—360^, and one of its anries = = ^^ -;

^ n n

this angle was obtained by the construction, in which the arc of

180 was divided into n parts and two of these parts subtracted.

This construction requires considerable care in drawing.

Octagon. — On the given side describe a square. Draw the
diagonals and produce them till the parts produced are equal to
the given side, thus giving two points of the polygon. Through
the extremities of the given side draw lines parallel to the
diagonals and make them also equal in length to this side. Thus
six points of the polygon are obtained, and the two remaining by
again drawing lines parallel to the diagonals of the square.

To draw a polygon by means of the sector, see paragraph 5.

Polygons of a greater number of sides can be constructed by
bisecting the arcs of circuinscribing circles subtending the sides of
polygons of half the number of sides.

Problem 19. 27. To reduce a given rectilineal figure to a triangle.

Let A, B, C, D, (fig. 7) be the given figure. Produce any side
AB, (most conveniently the longest side) both ways, as a base»
Draw a line joining the extremities B and D of the two sides BC,
and CD, one of which adjoins the base. Through the vertex C,
of the triangle thus made draw a line parallel to BD, meeting AB>
produced in d. Join Def, which line being substituted for the
twd original sides BC and CD will leave the area of the figure
unaltered, the triangle added to the original figure by this line Hd,
being equal to the triangle left out of it. Proceed in like manner

C.O.plj

fig4. /■

PRACTICAL PLANE GEOMETRY. 13

in regular order with the remaining sides, on each side of that
point which is selected to be the vertex of the resulting triangle.

The vertex of the triangle should be selected in the point at one
of the angles of the figure which by inspection would be judged to
bring the resulting triangle fts nearly equilateral as possible.

As the area of a triangle is equal to half the product of the
perpendicular Iieiglit multiplied by the base the area of any
irregular rectilineal figure can be readily obtained by this
problem.

28. To determine a line the square upon which shall be equal Paodlbm 20.
to a given Numerical area.

Make a line AB a linear distance equal to the number ex*
pressing the area. Produce the line, and make the part produced
BC equal to unity on the same scale. The mean proportional
between these lines, AB and BC (Prob. 15), will be the side of
the square required.

29. To construct a Square equal to any Kectilineal figure. Problem si.
Keduce the figure to a triangle (Prob. 19). Find a mean

proportional between half the base and the perpendicular of this

triangle. This mean proportional will be the side of the square

required.

If similar figures of any kind are described on the three sides of
a right-angled triangle as the homologous sides, the area of that
on the hjpothennse is equal to the sum of the areas of those on
the two sides. Hence the square or circle equal to the sum of two
or more given squares or circles may be found by this construction.

30. To draw a triangle similar to a given triangle but of a PaoBLm 22.
given area, nt^.

Draw a triangle ABC (Fig. 1, PI. 5) similar to the given
triangle, but without reference to area.

Draw a line from one extremity C of the base AC of this
triangle, and making any convenient angle with one side. Set off
on this line CM., a mean proportional between half th^ base AG,
And the perpendicular. Determine CN, equal to the square root
of the area (m^ by construction given in Prob. 20. Join BM.
Through N draw a line parallel to it meeting CB or CB produced
in D. Then drawing DE parallel to the side AB, to meet the
base produced^ if necessary, in E ; the triangle C D£ is that
required.

For the triangle ABC : EDC : : BC^ : D(?

::CM2:CJS2

But CM is the side of a square equal to the triangle ABC, there-
fore EDC is equal to the gqusre on CN or to m^ as required.

31. To construct a Eegular Polygon of a given area (Fig. 2). Pboblbm 28.
Let m^ be the given area. ^

Draw a polygon similar to that required, but without reference
to area.

Beduce the polygon to a triangle on one of the sides produced
as base, and whose vertex is one of the angular points of the
polygon. Determine by the construQ^ion in last problem a
triangle equal to the given area, whose vertex will be in one of

14 aSOMEXRICAL DBAWIXO.

tb^ sides^ or sides produced, of the first triangle. This vertex
will De one of the angular points of the required polygon. Other
angular points can be determined by drawing through this first
point lines parallel to the diagonak of the trial polygon, or by
4th Proportionals.

PftOBUui 24* 32. To draw an Ellipse from conditions.

(1.) When conjugate axes are given, the easiest method for
determining points in the curve is as follows (Fig. 3).

Draw through each extremity of the given axes lines parallel
to the other axis. Divide any half side of the parallelogram, thus
formed into any number of equal parts, and the corresponding half
conjugate diameter which meets this side of the parallelogram, into
the same number of equal parts. Number the two sets of divisions
correspondingly from the point of meeting outwards. Draw lines
through these points of division from the extremities of the other
conjugate axis, those from the extremity nearest the divided half
side of the parallelogram being drawn to the points in that half
side, and those from the other extremity through the points in
the half axis. The intersections of the pairs of lines drawn through
the points correspondingly numbered as above will be points in
the required curve. Points in the adjoining quadrant may be
determined by drawing any number of parallel ordinates to one of
the axes, and making the semi-chords on each side of the other
axis equal to one another.

(2.) If the axes given are the major and minor, that is those
bisecting one another at right angles, let AB and CD (Fig. 4) be
those axes, meeting in the point O. Mark off with a fine pencil
on the perfectly straight edge of a piece of drawing paper a
distance Mm equal to the semi-axis A O, and from M a distance
Mti equal to the semi-conjugate axis C 0. Then by revolving
the slip of paper, with the mark m always on CD and the mark n
always on AB, the successive positions of M will give a series of
points on the curve.

Proof. Let O A = M»i = a, O C =M« = ft, and Mp perpendicular
to OA = y, and Op = a? ; then m» : wM = 0» : np or, mn-f »M :

«M = 0«-h«p: np or, a : 6=07; */h^y^, or a^y'+ft^ a^=-o? h-,
the locus of which equation is an ellipse. The principle of
the trammel admits of gniphic illustration thus. From centre O
describe circles with radii equal to semi-major and semi-minor
axes. If on the larger circumference any point P (Fig. 4) be taken,
and this point be joined with the centre 0, and a line parallel to the
major axis AB be drawn from the point in the inner circumference^
where it is cut by the line PO to meet a perpendicular from P on
AB in the point M, then M is a point on the ellipse ; for if Mnm
be drawn parallel to OP it is evident since Vp and OC are parallel
that yirh and M« are respectively equal to OP or AO and OC, and
the line Mnm represents one position of the trammel, whose end
M (when applied as described above) traces the ellipse.

To find the major and minor axes of a given ellipse describe a
circle with centre that of the ellipse, and any radius so as to cut
the curve in four points. Join these opposite points by lines
through the centre and bisect the angles between them. The
bisecting lines will give the axes.

PBAOTIGAL SOLID aSOMETRT. 15

Section II. — ^Practigal Solid Geometbt.

33. By this term is meant that application of geometrical prin-
ciples by which points^ lines, and figures, not lying in any one
plane> may be clearly and accurately described by points, lines,
and figures projected on a plan^ surface.

These geometrical drawings are of two kinds, viz., perspectiye Projection,
or radial projection, and orthographic projection.

If a general idea alone is to be given, a perspective view is the Penpective
most suitable, because it corresponds with the picture which objects projection,
themselves make upon the eye. In this case lines or rays fix)m disaSSlnuigw
all the points of the soHd are made to converge to a vertex, repre-
senting the supposed position of a spectator, and to be intercepted
by a plane called the plane of projection (which is commonly
vertical) ; the outline is given by joining their points of intersec-
tion with this plane. But this outline is much distorted from the
original. Kot only are the edges of the solid foreshorten^ in
proportion as they are more oblique to the plane of projection ;
their length also varies with their distance nrom the vertex : and
therefore a double correction is necessary in order to ascertain the
true dimensions. The second of these sources of distortion may
be got rid of, however, if the vertex be assumed to be infinitely
distant, so that it is equally remote from all parts of the solid.
The rays, or projectors^ as thdy are termed, will then be parallel Projeeton.
instead of convergent, and all equal and parallel lines in the
object will be shown as equal and parallel lines in the drawing.

A projection under these conditions is termed orthographic, Onho^phic
and is most convenient for giving exact information of the dimen- projection,
sions of the object to be represented. Still the foreshortening
above mentioned remains, and a single projection gives no means
of ascertaining the true length of any lines that are oblique to the
plane of projection, because it does not indicate in any way the
relative distances of the several points from the plane. For this
reason it requires to be supplemented by a second projection upon
another plane inclined to the first These two planes are called
co-ordinate planes^ and for convenience they are assumed as hori- Co-ordinate
zontal and vertical, and consequently at right angles to one pl*n««.
another.

The projectors are assumed to be perpendicular to the plane of
projection in each case.

The point in which they meet the plane is the orthographic
projection of the point from which they originate ; and the posi-
tion of that point in space is fixed when its projections on both
horizontal and vertical planes are given.

The projection of a line will be the projection of every point
in this line, and of a solid, of all the lines forming the edges of
the solid.

The projection of any point, line, or solid, on a horizontal plane Flan and
is called the *' Pi?aw," and the projection on a vertical plane the elevation.

Elevation " of that point, line, or solid.

QBOMETUICAL DBAWING.

Ground line.

Section.

Profile.

Indices and
figured plans.

Representation
of snr&ces.

The plan or top vie\v of any object is the projection of all the
visible points of the object, or its model on the horizontal plane.

It follows, therefore, that the distance between any points in a
plan shows the true horizontal distance between these points,
while the elevation, which is a similar projection on a vertical
plane, shows the heights of the parts of the figure delineated

As the drawing can only be made on one plane, that is the sheet
of paper, the vertical plane is supposed to rotate (usually back-
wards) upon its intersection with the horizontal plane till it cotnes
into the horizontal plane. This line of intersection is termed the
Axis, Ground Line, or Line of Level, and is ordinarily marked ary.
The plan and elevation of every point will therefore always be in
the same perpendicular to the axis or ground line.

If a solid is cut by any plane, the plane figure formed by the
intersection of the surfaces bounding the solid, with the cutting
plane, is called the Section of the solid on this other plane.

TV^hen in military work the sectional plane is taken at right
angles to the crest or directing line of a parapet, &c. it is called a
Profile^ and this is the only section giving the real width of the
several pirts.

34. Instead of using the Plans and Elevations of any points of
a figure, the plans only may be employed, each point being
accompanied by a iiumbery expressing, in reference to soine given
unit of measure, the distance of that point from the horizontal
plane.

This number is termed the Index of the point, and when any
point has an index annexed, it is said to he figured.

The unit by which this distance is measured is that of the scale
of the drawing.

If the index of any point is zero, the point itself is in the
horizontal plane, and the point and its plan coincide.

If the index of a point is negative^ the point is situated helow
the plane, provided the positive indices express height ab&oe the
plane.

It is frequently necessary, as will hereafter be shown, to make
an elevation of any system of j)oints, given by iheiv figured plans ^
with reference to some given or assumed axis x g. This is done
by drawing projectors through the plans of the given points, at
right angles Uy xy, and setting up to fcale the length of the pro-
jectors, from X y, on one or the other side, according as the index
is positive or negative.

Conversely, if a system of points are given by their plans and
elevations, and it is required to attach to each plan the appropriate
index. Measure, to the scale of the drawing the distance of the
elevation of that point from the axis x y, and attach the resulting
number to the plan for the index, with a negative sign if the
original point is below the horizontal plane.

35. All objects which have to be represented in geometrical
drawings are bounded by geometrical surfaces^ which by their
mutual intersections form geometrical lines. And the plan and

PRACTICAL SOLID GEOMETRY. 17

elevation of any object consists of the plans and elevations of all
its edges or of these lines. These plans and elevations of the
edges are the lines drawn through the plans and elevations of all
the points of the edges.

But it is necessary to represent on the drawing the nature of
the surfaces themselves as well as the lines limiting them ; this is
done either by means of light and shade, or, more definitely in
some cases, by the application of the following principles.

All geometrical surfaces may be conceived as having been Generation of
eenerated by the motion of a geometrical line, in conformity with geoj^etncal

° , ^ ,.^. ° 7 / surfaces.

some law or condition.

Thus, a spherical surface is generated by the rotation of a semi- Sphere.
circle on its diameter considered as a fixed axis.

If an indefinite straight line always paaa through a i)oint, and
also through any curve whatever, both being fixed in position, the
straight line will generate a conical surface. If the curve is a Cone.
circle, the surface is that of the common cone, and if the line
passing through the fixed point and the centre of the circle is
perpendicular to the plane of the circle, the eurface is that of the
right cone.

If an indefinite straight line always pass through any curve Cylinder,
whatever, and also move parallel to a fixed straight line, the
former will generate a cylindrical surface. The common and
right cylinder are special cases of this, analogous to the common
and right cone.

A plane may be conceived as generated by the motion of an piane.
indefinite straight line always meeting another, and moving
parallel to a third straight line, both of these latter being fixed in
position.

Surfaces are represented in dra^vings by the projections of their
generating lines in their successive positions; and as most
surfaces admit of an indefinite number of modes of generation,
that form of generator and law of its motion is selected which
admits of easy delineation.

If any surface or surfaces, bounding a solid, be cut by a series Contours,
of equidistant horizontal, and therefore parallel planes, the inter-
sections are termed the contours of such surface or surfaces. The
contours of a plane are consequently equi-distant horizontal
parallel straight lines, which are called the horizontals of the
plane, anjd the plans of these will be equi-distant parallel lines.

An irregular or non-geometrical surface can only be expressed
with accuracy on a drawing by the plans of its contours. And
since in the operations of defilade and topography, constructions
on such surfaces are required, these constructions can be connected
with the problems of practical geometry by adopting the same
principle as for geometrical surfaces.

36. If a straight line always move perpendicular to a plane of Projecting sur-
projection, and pass through any fixed line, it will generate a ^*^®*'
surface called the projecting surface of that line, and the projection

GEOMETRIOAL DRAWING.

ProjectlDg
plane.

Traces.

Notation.

G^eral re-
marks.

of the fixed line is obviously the interaeoiion of this projecting
surface with the plane of projection.

If the original line is a straight line, its projecting surface is
obviously a plane, and is called the projecting plane of that line.

It may be here remarked, that the perspective projecting surface
of wy original curve or solid is a conical or pyramidal sur&ce,
while the orthographic projecting surface of sucn a line, or of any
solid, IS a cylindrical or prismatical surface.

The points or lines in which any line or surface cuts the planes
of projection are termed the traces of that line or surface, and are
distinguished as the horizontal or vertical traces according as they
lie in the horizontal or vertical planes.

37. To obviate the confiision arising from the number of lines
unavoidable even in comparatively smiple constructions, a con-
sistent notation must be employed, by the use of which the
different lines may be distinguished.

When indices axe employed, the plan is sufficiently distinguished,
since no index can ever be affixed to an elevation, but even in
this case it is better also to use letters if any ambiguity can be
avoided by so doing.

Constructions are also made more distinct by a proper and
consistent use of dotted lines of different kinds, but it would be
useless to give any rules for their employment, as this must be
left to the judgment of the draughtsman.

8ince no line can be considered given or determined unlel^s
two points of it at least are figured, or its elevation be given, a
line not so distinguished always indicates a vertical plane, and a
point unaccompanied by an index or by an elevation expresses a
vertical line. It is obvious that this unfigmred line or point is the
trace of the vertical plane or line.

The chief thing to be attended to, as regards notation, is that
it must be consistent throughout the same drawing. But any
kind of letter, capital or small, may be used at the pleasure of
the draughtsman, and any mode of distinguishing the elevation
from the plan of a point, line, &c., provided he preserves the
same character throughout to signify the same thing.

The letters a and a' are usually employed to express the
plan and elevation respectively of a point A In space : a b and
a^ b' the plan and elevation of a line A B.

38. The elementary problems of practical solid geometry are
generally solved by making an elevation of the data, when these
consist of figured plans, or by constructing a plane.

A plane is said to be constructed when the plans of any points,
lines, or figures, lying in that plane, are drawn on the supposition
that the plane has been turned round on a horizontal of the plane,
carrying with it all points and lines contained in it. A line is
"constructed'' when it is drawn on the supposition that its
projecting plane is turned round on its intersection with a hori-
zontal plane till coincident with it.

Whenever an elevation has to be made, and a plane is part of

FBAOTICAL SOLID GBOMETRT. 19

the data, the Une of level slioukt be ai riaht angles to the horizoniaU
of that plane; because in that case the plane beine as it were
seen edgewise its true inclination is shown^ and its ele^ation^
which would otherwise be an indefinite surface, is made to concide
with its vertical trace;

The term mclinatton is always used to express the angle which lAeliontion.
a line or plane makes with the horizontal plane.

The plan and elevation of any point P, in a ffiven line AB
must obviously be points (p) and (j)') respectively in the plan
(a i) and elevation (a' h') of the line.

Two lines do not necessarily meet because their plans cross InterHc-ctioo.
one another. Whether the lines really do meet or not, is ascer-
tained by determining whether the index of the common point
in the plans, which will apply to one of the lines, will apply
equally to the other.

Whether two such lines meet or not can also be ascertained by
making an elevation of them on any line of level. If the point
in which the elevations of the lines cross one another, and that
in which the plans intersect, are found to lie in one line perpen-
dicular to the line of level, the lines meet, but not otherwise.

Two lines are not necessarily parallel because their plans are Paruiielism.
paralleL The criterion of parallelism is that equi-distant points
in the plans of each have equi-different indices, increasing in the
same direction.

An analogous test determines the parallelism of two planes,
which is not to be inferred from that of their horizontals only,
but is determined by observing whether equi-distant horizontals
have equi-different indices, increasing in the same direction.

These remarks on parallelism obviate the necessity for making
separate *^ problems " of two such simple constructions as those
required for drawing a line or plane, to be parallel to a given line
or plane.

A plane is implicitly given by the figured plans of any three
points in it, but more conveniently by the plans of two of its
horizontals.

A line drawn at right angles to the plans of the horizontals of Scale of a
a plane, and figured with their respective levels at the points of P^* '
meeting them, is called the scale of that plane, and is doubled,
like an ordinary scale, to prevent confusion with other lines on
the drawing.

If a line lie in a plane the indices of any points in the line must
be the same as those of the horizontals passing through those
points.

The angle which a. line makes with a plane is evidently mea-
sured by that which the line makes with its orthographic
projection on that plane.

The term vertical is, of couse, used to express a line or»plane
perpendicular to the horizontal plane.

The use of indices simplifies ihe construction, because with them
many problems can be wholly worked out on the plans, or horizon-
tal projections ; and in any case such elevations only as are absolutely

lane.

GEOMETRICAL DRAWING*

necessary to solve a problem need be made, and those not till they
are required. Especially when the vertical distances of the several
points from any horizontal plane vary but little from each other
as compared with their relative distances in horizontal directions,
as is generally the case in drawings of fortifications or representa-
tions of country, this method of indices, termed horizontal pro-
jection, is preferable to that in which all points arc given by
their projections on two co-ordinate planes. It will, therefore
be applied in the solution of the elementary problems that follow.
(Para. 47, &c.)

Projection of Oeometrical Solids,

39. The more simple regular solids, i,e. the Tetrahedron, Cube,
and Octahedron, and prisms, pyramids, spheres, cones and cylinders,
afford good exercises in projection.

The following cases comprise sufficient data for the projection
of any of these : —

1. When one face of the solid is in or is parallel to the hori-
zontal piano.

2. When one edge is in or is parallel to the horizontal plane^
the inclination of a face containing this edge being given.

3. When the inclinations of one face and a line in that face are
given.

4. When the inclinations of two edges or diagonals are given.

5. When the inclinations of two faces are given.

At present only the first two cases will be considered.

40. The tetrahedron is a regular solid boimdedbyfour equilateral
triangles. The plan of the solid when resting on a horizontal plane
will be an equilateral triangle, the plan of the apex being at the
centre of the triangle. ITie height of the apex may in this case
be determined from the plan. Per the inclined edges of the solid
are really equal in length to the edges of the base, but their length
in plan is the distance from the centre to the angles of the base.
If, then, a right-angled triangle is constructed having the real
length of these edges as its liy[)othenuse and their apparent length,
in plan, as its base, the third side of this triangle must correspond
to the height of the apex.

The cube requires no explanation.

The octahedron is a regular solid bounded by eight equilateral
triangles. Its plan when one face is in or is parallel to the hori-
zontal plane will be a regular hexagon formed by two alterna-
ting equilateral triangles of given side. Its height, like that of
the tetrahedron, is derived from the side of the solid.

Prisms and pyramids may be of any given base and height,
may be right or oblique, and are solids bounded by plane faces.
Spheres, cones, Spheres, cones, and cylinders, whos.e generation has been
and cylinders, previously explained, are solids of revolution.

41. In Plate 6 are shown two solids projected as examples of
cases 1 and 2.

Tetrahedron.

Cube.
Octahedron.

Prisms and
pyramids.

i.!>x.§eE!i«dli2.B tfcrd S* Co-reniUrRrdexi

PRAOTIGAIi SOLID Oi!:OMBTRX. 21

Case 1 is illustrated (Fig. 1) by the plan of a double hexagonal
right pyramid which rests with one £ice on the horizontal plane.
To enable this figure to be drawn the solid is first drawn in plan
as if the common base of the two pyramids were horizontal. An
elevation of the solid in this po:«ition is then drawn on a ground
line perpendicular to one edge of the base. In elevation the solid
is then turned round on this edge as a hinge till the face containing
this edge is horizontal, te, till the vertex of the pyramifl comes on
the ground line. This elevation being projected, the plan of the
solid in the required position is obtained, the line a b being
common to the plans of both positions of the solid. Any desired
elevation of the solid in this position can be obtained by drawing
a suitable x y line representing the position of a vertical plane
on which the projection of the solid is required. The plans
and elevations of the solid required during construction of the
problem are termed auxiliary plans and elevations. They have
been shown in the plate in dotted lines.

Case 2 has been illustrated (Fig. 2) by the plan of a pentagonal
right prism which rests on one edge in the horizontal plane and
has one of the faces containing that edge inclined at a given angle %.
In this case an auxiliary end elevation in accordance with the
data is first drawn and the plan of the solid projected from this
elevation. An elevation on a given vertical plane has also been
shown.

42. If a solid is cut by a plane, the plane figure contained by Sections of
the straight or curved lines in which the plane cuts the surfaces of ^^l*^-
the solid is, as already mentioned, termed a section.

The form of the section depends not only on the nature of the
containing surfaces of the solid, but also on the position of the
secant plane with respect to the solid.

The sectional elevation or plan of a solid, is the elevation or
plan of the section and of such portions of the solid as would be
visible when projected on the secant plane, or a plane parallel to
it. Thus in Fig. 2, PI. 6, the plan of the prism has been cut by
two parallel secant planes, and the true form of the section is shown
on the plane of elevation parallel to the secant plane. In each
case those parts of the solid which lie in front of the secant planes
being supposed to be removed, the elevation of the remainder
together with the section seen in its true form constitutes a
sectional elevation.

Evidently, therefore, two sectional elevations will always be
possible, according as one side or the other is regarded as in front
of the secant plane. The intended point of view is, however
commonly indicated by the direction of the letters attached to the
line of section.

_ «

The section of a figure contained by plane surfaces is always
rectilinear in form, but the section of a solid contained by curved
surfaces may be either in whole or in part a plane surface bounded
by curved lines. Thus the section of a sphere is always a circle,
while that of a cone may be either a triangle (if the secant plane
passes through the vertex), or a circle (if the secant plane is at

OEOMETBICAIi DBAWINO.

Interpenetra-
tion of solids.

Shadows.

Shade lines.

right angles to the axis), or an ellipse (if the secant plane makes
with the axis an angle greater than that made by the generatrix
or slant side of the cone), or a parabola (if the secant plane is
parallel to the generatrix), or finally^ a hyperbola (if the secant
plane is inclined to the axis at a less angle tban the generatrix.)

43. It is often necessary to represent the intersections of solids
one with another.

A general method for determining the intersections of any two
interpenetrating solids is to contour both of them by horizontal
planes, and since the contours of the same level on each solid
must intersect (if they intersect at all within the limits of the
surfaces of the solids) in points which are on the intersections of
the two solids, the form of these intersections can be obtained to
any required degree of accuracy.

Solids composed of curved surfaces as well as those contained
by plane surfaces may be so treated. The investigation of the
intersections of solids composed of curved surfaces is, however,
often simplified by taking a series of secant planes which are not
horizontal. And in general that particular system of planes or
surfaces whose intersections with the given solids are most readily
determined should be selected in the investigation of the intersec-
tion of interpenetrating solids.

44. Delineated shadows are used in orthographic projection
to define more clearly the form of an object. If rays of light
proceeding mutually parallel illuminate a solid in space, the solid
intercepts a portion of these rays. These intercepted rays will
form either a prism or a cylindrical surface enveloping the solid.
The intersection of this prism or cylinder of shade with auy plane
or planes interposed will be the shadow of the object intercepting
these rays.

The line of contact with the solid of the prism or cylinder of
intercepted rays will divide the solid into an illuminated and an
unilluminated portion. In solids contained by plane surfaces
these portions can usually be distinguished by inspection; in
solids contained by curved surfaces it is more difficult to do so.
On the cone or cylinder, however, the lines of separation will be
generatrices ; on the sphere, a great circle.

From a consideration of the above remarks it is evident that
to determine the shadow cast by any solid on other surfaces, we
must determine the intersection, subject to given conditions of
direction of light, ef certain lines and planes with those surfaces.

The convention regarding direction of light, which is generally
employed for delineating shadows, is to assume both in plan and
elevation that the light comes from the left-hand upper 'comer of
the drawing paper, and makes with the ground line both in plan
and elevation an angle of 45^.

45. Shade lines are dark lines on those edges of a solid which
would throw shadow on the supposition of a conventional direction
of light. They are employed to give definition when the shadows
themselves are not shown, and should therefore not be used when
shadows are drawn.

PRACTICAL SOLID GEOMETRY. 23

Shade lines Bhould not be employed at the intersection of a Shade Uom.
light and dark surface when the latter is visible.

The outline of a curved surface should not have a shade line.

46. Shading is also employed to ^ve definition to an object. * °^*
There is more than one convention regarding direction of lights but
that which is simplest in use^ and in general most suge;estive9 is to
suppose the light to flow or fall at right angles to the plane on
which the object is projected, and to make those surfaces lightest
which are at right angles to the direction of lights and to darken
the other surfaces in <Urect ratio to their inclinations to this
direction.

To shade the elevation of a solid on this system it will be suffi-
cient^ as in the elevation of the prism in Fig. 2, PL 6, to take
two vertical secant planes^ parallel to the vertical plane of pro-
jection^ and obtain on the elevation the elevations of the sections ;
the breadths of the section band on each plane of the solid in
elevation will show inversely the relative ^amount of shade that
these planes will carry.

To shade the plan in a similar manner two horizontal planes
should be employed

Spheres are the solids to which this system of shading is least
applicable^ and it is advisable to adopt in shading them some other
convention regarding direction of Ught. Of course, idso, where
shadows are shown, the same convention must be adopted to
regulate both shade and shadow.

Elementary Problems in Solid Geometry.

47. To place in a given plane a line making a proposed angle Pboblem i.
with the horizontal plane.

Liet M be the scale of the given plane^ and 9 the proposed incli-
nation of the line (Fig. 1^ Fl. 7). It is required to determine
the plan of a line that shall lie in the given plane^ and make the
angle B with the horizontal plane.

Draw a right angled triangle, whose perpendicular is any con-
venient number of units n (from the scale of the drawing) in
length ; and whose hypothenuse makes the angle B with thebase.
The base thus determmed is the plan of a line having the required
inclination, and whose extremities differ in level by the height of
the perpendicular of the above triangle. And this length of base,
placed so as to meet the plans of two horizontals of the given
plane5 having a corresponding difference in level, will be the plan
of a segment of a line, lying in the given plane, and having the
required inclination.

Two such lines can be drawn lying in opposite directions, unless
the angle B is the same as the inclination of the plan, when only
one can be drawn, viz., at right angles to the horizontals of the
plane.

If the angle B were greater than the inclination of the plane,
the problem would evidently be impossible ; for no line can lie in

GEOMETUICAL DIIAWIXG.

Problem 2.

Problem 8.

Problem 4.

a plane, and make a greater angle with the horizontal plane than
that which the plane itself maked with it

Instead of making the right angled triangle above described^
the tabular cotangent of the proposed inclination to radius of the
difTerence in level between the two horizontals may be taken^ and
this distance set off as before, between the plans of tiie horizontals,
as it is evident that the plan of any finite line is equal to the
cotangent of its inclination multiplied by the difference in level
between its extremities.

48. Through a given line to draw a plane to make a proposed
angle 6 with the horizontal plane.

Let fls, ^43 (Fig. 2) be the plan of the given line, determine any
two convenient points, say those whose indices are 20 and 30 in
the given line. Suppose the point 30 to be the vertex of a right
cone whose side has the inclination of the required plane, and
whose base is horizontal and at the level 20. Then the required
plane will be tangent to this cone, and its horizontal 20 will be
tangent to the base of the cone, and will pass through the point
20 in the given line. Therefore to determine the base of the cone
draw anywhere a right angled triangle whose perpendicular is
equal to the difference in level of the above two points, itff
hypothenuse making the given angle 6 with the base. From the
point 30 with a radius equal to the base above determined, describe
a circle, and from the other point, 20, draw tangents to this circle,
they will be horizontals at the level, 20, of the required planes, as
this problem has a double solution. Through the point 30 draw
parallels to these lines, a second horizontal in each plane will thus
be obtained and their scales can be graduated as required.

If 6 is less than the inclination of the given line the problem
would be impossible ; if equal to it, only one plane would fulfil
the conditions.

49. To determine the scale of the plane containing three given
points.

Let «4i, ^25, and c^ (Fig- 3) be the plans of the three points.

Find in the plan a, c, of the line joining any two of the given
points (most conveniently the highest and lowest) the plan of a
point of the same level as the third point and join it with this
latter. This line will evidently be a horizontal of the required
plane and the scale can be drawn anywhere at right ang es to it,
and graduated by horizontals (parallel to the first) through either
of the other given points.

A plane is implicitly given or determined by any three points not
in the same straight line being known, but to represent the plane on
a drawing, so as to show its direction and inclination, it is neces-
sary to determine the plans of at least two of its horizontals.

50. Through a given point to draw a plane parallel to a given
plane.

Let M (Fig. 4) be the scale of the given plane, and p^ the plan
of the given point.

As the required plane is to be parallel to the given plane, its
horizontals thII be parallel to those of the latte?^ and consequently

PRAOTIOA.L SOLID GfiOMETBY. 25

its scale may be drawn anywhere parallel to the scale M. A
horizontal drawn through the point p will determiDC on the scale
the point of division of this level (24) on the scale of the required
plane^ and from this pointy 24, graduate the scale similarly to the
scale M ; that is, for equal distances on plan figulre equal differ-
ences in level towards the same direction.

51. To determine the intersection of two given planes which Faoiutic 5«
are not parallel to one another.

Let M and N (Fig. 5) be the two planes represented by their
scales.

(I.) Draw any two convenient horizontals through similarly
figured divisions of the respective scales. Their intersections will
be the plans of points lying in each of the two planes, and there-
fore the line drawn through these points will be the plan of the
line in which they intersect.

(2.) If two planes, not parallel, be cut by any third plane
whatever, it is evident that the intersections of this third plane
with each of the original planes will meet in a point in the inter-
section of the original planes, unless they are parallel to that
intersection.

If, therefore, from the figures of the scales of the given planes
two pairs of similarly figured horizontals cannot be obtained to
intersect within the Umits of the drawing, assume any two con-
venient auxiliary planes, by drawing any two pairs of parallel
lines and fiorurin<:: them as suitable horizontals. Determine the
intersections of the first assumed plane with the two given planes,
the point where these intersections meet will be a point in the
intersection of the two original planes. Repeat this operation
with a second assumed plane, and the point in which this second
pair of intersections meet will determine another point in the
required intersection of the original planes. (Fig. 5b.)

(3.) When the horizontals of the given planes which meet are
parallel to one another (Fig. 5a), the intersection will be a line
parallel to the horizontals, and can be most conveniently deter-
mined by making an elevation of both the planes on .any line of
level at right angles to the horizontals, the intersection of their
elevations will be the elevation of the required line ; and a line
drawn through it, and figured by mieasuring its height above or
below the line of level, will be the plan of the required line.

52. To determine the point in which a given line meets a given Faobuui 6..
plane.

Let a^, h^ (Fig. 6) be the plan of the given line, and M the
plane given by its scale.

(1.) The intersection of a line with a plane will be a point
conunon to the given line, and the line in which any plane con-
taining the given line meets the given plane. And the plan of
the required point of meeting will be the common point in the
plans of the above-mentioned lines.

Assume therefore any convenient plane containing the given
line, by drawing through any two figured points in the plan of the

42642. Q

GEOMETBIGAL DBAWINO.

Contoured
works.

Une a pair of parallel lines in any direction as corresponding hori-
zontals of the assumed plane. Determine (Prob* 5) the plan of
the intersection of this assumed plane with the given plane M.
The point in which this latter Une outs the plan of the given line
will be the plan of the required point, which being in the plane
and line can be figured from either.

(2.) The above is generally the most convenient method, but
the point of intersection may also be determined by making an
elevation of both plane and line on a line of level at right angles
to the horizontals of the plane. The point in which these eleva-
tions meet must be the elevation of the point of intersection of
the line and plane, its plan, in the plan of the given line, being
determined by a perpendicular to the line of level through the
elevation of the point, 2jdA figured from the scale of the plane or
line.

53. The foregoing problems, more especially problems 1, 2,
and 5, are those which are made use of in ordinary fortification
* drawing and contouring.

A figured line, sometimes the crest line of the work, sometimes
the intersection of one of its slopes with the natural ground, is
generally the starting point. Through this line a plane (or slope)
of given inclination is to be drawn (by Prob. 2) ; the inclination
of the plane being commonly indicated by a fraction expressing
the tangent of the angle.

The slope so obtained will either be bounded by a line drawn
at a fixed distance, in which case the bounding line will serve as
the starting point of a fresh slope ; or else it will be terminated
by intersection with some other slope (by Prob. 5), whose contours
have been similarly found.

This is continued until all the slopes are shown by their contours,
and their intersections with each other and with the natural
ground are determined.

Sometimes, instead of the true inclination of the slope being
given, its profile inclination, measured in a vertical plane perpen-
dicular to the plan of the crest line, is given, as being the more
material In this case Prob. 3, instead of Prob. 2, must be used
to find the horizontals of the slope."^

Fboblsm 7.

Further Problems in Solid Geometry.

54. To draw a line through a given point perpendicular to a
given plane.

Let/?46 (Fig. 1, PI. 8) be the plan of the given point, and M
the scale of the given plane.

If a line is perpendicular to a plane, the plan of the line will
necessarily be perpendicular to the horizontals of that plane.
Hence a line drawn through the plan of the given point perpen-
dicular to the horizontals of the plane M (or parallel to its scale),
will be the indefinite plan of the required perpendicular. Make

* The obligatory part of the course of solid geometry ends at this point.

Fig. 1.

P
4*5

7''

/
/

29-5

- 1--

_X(20)

Opp.'to-pag^ J^ .

PBAGTIOAL SOLID aEOKETST. 27

an elevation of the given plane^ and pointy on any line of level at
right angles to the horizontals of the plane^ (the indefinite plan of
the perpendicular may be conveniently used, assuming it at any
suitable level,) draw a perpendicular p' q to the elevation of the
plane from the elevation of the point. The point q' in which this
perpendicular meets the plane will be the elevation of the point in
which the perpendicular from the given point meets the plane.
And its plan (^) will be determined in the plan of the line ahready
drawn by a perpendicular to the line of level through the eleva-
tion q\ and can be figured from the scale of the plane or by
measuring the length of the perpendicular between the line of
level and the elevation 9' on the scale of the drawing.

The magnitude of the divisions or any required number of
divisions of the scale of any line or plane is as before steted
(Prob. 1), the cotanffent of the angle at which tiie line or plane
is inclined, to the radius of the unit or any given number of uoiti
of the scale of the drawing.

Hence, if a line and a plane are mutually perpendicular to each
other, the angles at which they aie inclined to the horisontal plane
being the complements of each other, the divisions of the scale of
the one will be to those of the other as cot : tan. Therefore the gra-
duation of a line perpendicular to a plane, or the converse, may be
determined without making an elevation as in the foregoing, for
by similar triangles the reomred divisions will be a third propor>-
tional to the ratio between those of the given plane or line mtamKred
on iht scale of the drawing, and the numerical unit. Thus if 10
divisions of the scale of the given phme measure 14 units on the
scale of the drawing, as 14 : 10 :: 10 : 7* 1> then 7* 1 measured on
the scale of the drawing will be the dimension of 10 divisions on
plan on the line perpendicular to the given plane.

55. To draw a plane through a given point perpendicular to a PBoaum s.
given line.

Let a^ b^ (^^g* ^)> he the given line, and p^ the given point.

This problem is the converse of the last, and the solution is
similar.

The required plane being perpendicular to the given line, its
scale may be drawn anywhere parallel to the plan of the line.
And as it is to contain the given point p^^ the division 30 of its
scale will be determined by a horizontal through the plan of the
point.

Make an elevation of the given line and point on a line of level
perpendicular to the horizontals of the plane (the plan of the line
may be conveniently used and assumed at level 30). Then draw
through the elevation of the given point (p') a perpendicular
ip' 9^)9 to the elevation of the une. This perpendicular wiU be
the elevation of the required plane, and the scale can be graduated
&om it. Or, without making an elevation, (see note, Prob. 7,)
supposing that 10 divisions on the scale of the line measure 7*5
units on the scale of the drawing, 7*5 : 10 :: 10 : 13*3, therefore
10 divisions of the scale of the required plane =13*3 units of the
scale of the drawing.

56. To measure the angle formed by two lines which meet Pboblbm 9.

O 2

GEOMETBIGAL DBAWING.

I4^t flio, Cgg, and

Problem 10.

&15, c^ (Fig. 3), be the plans of two lines
meeting in the point c.

The angle contained by these lines can only be measured in the
plane in which they He, therefore by constructing this plane, that
is bringing it into the horizontal, the angle will be represented in
its true form.

Draw from b a line to a point {k) of the same level (15) in the
line a c ; this line b k will be the plan of a horizontal of the plane
in which A C and B C lie, and can be used as an axis on which
to revolve the plane. Draw through c a perpendicular to the
horizontal b A, meeting it in/. The point C will, when brought
down to the horizontal plane, be found in this perpendicular
produced, as it must move in a vertical plane perpendicular to the
horizontal b k. Its distance from/ will obviously be the length of
the hypothenuse of a right angled triangle whose base is f c and
perpendicular c c\ the difference in level between the point c and
the horizontal b h. The true angle required will be A C &.

The true angle could evidently be obtained by making a
triangle with three lines equal to the true lengths of the lines
A C, C B, and B A, but not so conveniently as by the above
construction.

57. To measure the angle contained by two planes which meet
one another.

Let M and N be the scales of two planes which meet. (Fig. 4.)

Determine the intersection (/ m) of the planes M and N
(Prob. 5).

The angle required is measured in a plane perpendicular to
that intersection. Draw, therefore, a line 1 1^ at right angles to
/ m, to meet similarly figured horizontals of M and N. Let this
be the plan of a horizontal of tlie plane of measurement ; its level
being the same as that of thQ horizontals it meets. Make an
elevation of the line I m, and of the plane of measurement (the
latter being drawn through the vertical trace of 1 1, and perpen-
dicular to r 7w'), and so determine the plan (q) of the point in
which the line meets the plane. Then t q and t^ q will be the
plans of the intersections of M and N with the plane of measure-
ment, and the angle t q t^ will be the plan of the contained angle
required, which can be constructed and measured as in the last
problem. In making the above elevation, the plan of the inter-
section (/ m) may be conveniently used as a ground line, at the
level of the horizontal 1 1^.

By the application of this problem a plane can be drawn
through a line lying in a given plane so as to make a proposed
angle with the given plane.

Problem 11. 58. To measure the angle which a given line makes with a
given plane.

Let M be the scale of the given plane, and a^^ b^, the plan of
the given line (Fig. 5).

The intersection of the line with the plane is first determined
(Prob. 6) t — .

PRACTICAL SOLID GEOMETRY. 29

A perpendicular is then drawn from any point in the given line
{as a) to meet the given plane at p (Prob. 7). The angle p i ais
the plan of the required angle, and is measured by constructing
the triangle p i a (Prob. 6).

If the given line is horizontal (Fig 9.)> the triangle p t a is at
once constructed by describing a semicircle on a i, and through p
drawing a perpendicular to the horizontal a t to meet the circum-
ference in P. By joining P i, the angle is obtained.

59. To draw the plan of any right-lined figure when its plane i:5 Problem 12.
inclined at a given angle.

Let A B C D (Fig. 7) be any plane figure, and B the angle at
which it is to be inclined.

Draw any line Z n as the horizontal trace of the plane in which
the figure is to lie. Draw a ground line xy perpendicular tothis^
and a line / m making the given angle B with z y as the elevation
of the plane.

If the plane of the figure be revolved, or lifted up on the
horizontal trace as an axis^ till it coincides with the plane whose
vertical trace is / m^ the various points A B C D of the figure will
move in vertical planes perpendicular to the horizontal (/ n).
Draw, therefore, through A, B, C, and D, lines perpendicular to
/ n. Set off along the vertical trace / wi, distances / a\ I b\ I c',
i d\ equal to those of A, B^ C and D^ from I n. And from a'y b\
c\ and d! , draw perpendiculars to the xy line to meet those drawn
in plan through A, B, C^ and D. The points in which the
respective perpendiculars meet will determine the plan of the
figure A B C D, when lifted into the plane mln.

This is the converse of constructing an inclined plane figure
whose plan is given.

60. To draw the plan of any right-lined figure, when two of Pboblim 13.
its sides, meeting one another, are inclined at given angles.

Let ABODE (Fig. 8) be any plane figure ; it is required to
determine its plan when the side DE is inclined at 30^ and the
side DO at 35^

At any convenient point in DE, or DE produced, make the
angle D h /= 30^, and from D draw a perpendicular D / to A /.
With D as centre with radius D /, describe an arc, and draw m t^
a tangent to this arc, and making the angle 35^ with DC at the
point U Then h I and m t are evidently the plans of the segments
D h and D t inclined respectively at 30^ and 35^, and h t will be
a horizontal of the plane in which they lie. The elevation of this
plane may be drawn by taking a ground line x y, at right angles
to this horizontal, cutting it at a point /. Draw a line o, o, at the
distance = D / from the ground line, and cut this line o, o, in d! with
the distance D r=the perpendicular from D to the horizontal t h
described from the point r' : d' r^ will be the vertical trace of the
plane of the figure, d' r' x' being its angle of inclination. Draw
the line d d perpendicular to ^ y to meet D r in £?; d will be the
plan of the point D when raised into that plane. The remaining
points of the figure can now be determined as in last problem.

OEOMETBICAL DRAWING.

PbOBLBM 14.

PSOBLBM 15.

The sum of the angles of mclination cannot exceed the difference
between 180^ and the angle contained by the two lines D hD t,
and if eqnal to this difference the figure would evidently lie in a
vertical plane.

This problem deals with the preliminary steps required for
case 45 noticed under the projection of solids.

61. Given the inclination of one face of a cube, and of a line
in this face^ as one of the edges^ or a diagonal^ to draw the plan of
the solid.

Let the plane of the face A B C D (Fig. 1, PI. 9) be inclined at
55°, and one of the edges of this face at 40°.

Represent a plane inclined at 66° either by its vertical and
horizontal traces, or by drawing any two of its horizontals^.

Place in this plane a line inclined at 40° (Prob. 1).

Construct this line, and set off on it the length AB of the edge
of the cube.

Draw a square A B C D upon this side, and determine (by
Prob. 12) the plan a, d, c, d, of this square when inclined at 66^.
The edges of the cube which are perpendicular to this face, will in
plan be at right angles to the horizontals of the plane, through
the points a, ft, c, d. Their lengths will be determined by an
elevation.

If the diagonal were given, its true length would be set off on
the above constructed line, and the square A B C D made upon
it. If; instead of a face and a line in that face, the inclination of
two lines of a face is given the plan of the face and its inclinatiors
are determined as in Prob. 13, and the plans of the remaining
faces are then determined as above.

This problem corresponds to case 3 noticed under the pro-
jection of geometrical solids.

62. To draw a plane through a given line to make a proposed
angle (6) with a given ])lane.

This problem is similar to Prob. 2, only that the given plane is
not assumed to be horizontal in this case.

Determine first the point in which the given line meets the
given plane (Prob. 6). Let i (Fig. 2) be the plan of this point of
meeting. Take any point p in the given line, and determine a
perpendicular {p q) to the given plane (Prob. 7). Suppose this
perpendicular p q to be the axis of a right cone, with p as its
vertex, and its base resting on the given plane, its slant side
making the proposed angle ($) with the plane.

It will be evident that a line drawn through the point i in which
the line meets the plane, and touching the base of the cone sup-
posed as resting on the plane, will be the intersection of the
required plane with the given one, and the scale of the former can
be obtained.

In order to draw the line of intersection above mentioned, make
an elevation of the point p^ and of the given plane. From p' (the
elevation of the point p,) draw a line p' r', making the angle $
with the elevation of the given plane. The^ p' r' will be the

PBAGTICAL SOLID OEOMETBT. 31

elevatioii of the slant side of the cone, of which p^ ^ ib the bmib,
and q^ r, the plan of a radius of the base, will be the semi-minor
axis of the elhpse into which the circular base of the cone, resting
on the given plane, will be projecting upon the horizontal pLme.
The semi-major axis being equal to the radius of the base of the
cone, the ellipse can be drawn. A tangent to the ellipse from the
point i can now be drawn, and the point of contact k, figured from
the scale of the given plane. The scale of the required plane can
now be determined as containing the line i k, and the given line
(Prob. 3).

The point of contact k will be most accurately determined by
constructing the point I, and the circular base of the cone and
determining the point of contact K of the tangent from I to the
circle, and again lifting K into the given plane, the point k will be
obtained without drawing the ellipse.

As there can be two tangents drawn to the base of the cone,
two planes can be determined fulfilling the required conditions.
The angle must not be less than the angle which the given line
makes with th6 given plane.

63. To draw a plane through a given point, to have a given Phoblkii is.
inclination (^), and to make a proposed angle {6) with a given plane.

Let p (Fig. 3) be the plan of the given pointy and M the scale
of the given plane.

Suppose the point P to be the conunon vertex of two cones,
one, as iq the last problem, resting on the given plane, with its
axis perpendicular to, and its slant side making the proposed
angle ($) with it ; the other also a right cone^ but resting on the
horizontal plane, and its slant side having the inclination (^). The
required plane will contain the point P, and will touch both these
cones.

Determine the horizontal traces (on any convenient level) of the
above-mentioned cones, that of the first will be an ellipse or other
curve, the other will be a circle. The line then drawn touching
both these curves will be a horizontal of the required plane at the
assumed level, and the point P, being also in this |)lane, the scale
can be graduated.

If the horizontal traces of both cones intersect5 there can be
two planes determined as fulfilling the conditions ; if they are
clear of each other, four ; if they touchy three ; while if one falls
inside the other, no plane can be drawn.

64, Given the inclination of two faces (or of a face and an end) Pboblbm 17.
of a regular solid to determine its plan.

Let the solid be a right prism of five sides; the inclination of
one end to be 70°, and of one face 50°.

Take any line, s^ x y (Fig. 4), and draw the vertical and hori-
zontal traces of a plane inclined at 50°, and at right angles to the
vertical plane. Take any point in this plane, and from it draw a
line at right angles to the plane. Determine (Prob. 2) a plane con-
taining this line, and having the given inclination 70° to the horizon.
This latter will be the plane of the base of the prism, being drawn
through a line perpendicular to the plane of the side (that given as

32 OEOMETBIGAL DRAWING.

inclined at 50^). Determine the intersection of these two planes
(Prob. 5). It will contain nn edge of the solid. Construct this
line of intersection as lying in the plane of the base. Set off on it
a length equal to one side of the given prism, and on it draw a
pentagon of given dimensions. Lift this pentagon into the plane
of the base, and the plan of the base will be determined. Con-
struct the edge of the figure as lying in the plane of one side (that
given, inclined at 50°), and draw on it a parallelogram equal to
the side of the prism. Lift this parallelogram into the plane of
the side, and the plan of that side will be determined. The
* remaining sides of the solid will be easily completed by parallel
lines.

This problem corresponds to case 6 noticed under the Projection
of Geometrical Solids.

Problem 18. Qg^ Xo draw a line perpendicular to two given lines which are

neither parallel nor meet one another.

Let a b and c d (Fig. 5) be tlie plans of the given lines.

Determine a plane containing one of the given lines a b and
parallel to the other <»iven line, by drawing from any point in the
first line a line parallel to the other, and then (Prob. 3) a plane
containing these two lines.

Draw from any point (r) in the second line, c rf, a perpendicular,
r s, to the plane thus determined (Prob. 6), and detennina the
point (s) in whicli it meets the plane. From this latter point (s)
draw in the plane a line, s t, parallel to the second line, c d. It
must meet the fiist line, as it lies in the same plane with it, and
cannot, by the conditions, be parallel to it. From the point of
meeting, f, draw a line, t v, parallel to the perpendicular, r s. It
must meet the second line, since it lies in the same plane with cd
and s t Hence t v is perpendicular to both the given lines a b
And c d.

Isometric Projection,

66. Isometric projection is an application of orthographic pro-
jection, which may be conveniently applied to the representation
of objects, such as buildings, machinery, wood work, &c., whose
dimensions lie principally in planes mutually at right angles.

In this kind of projection the plane of projection, instead of
being taken^ vertical or horizontalj^ is assumed to be equally inclined
to the three principal axes at right angles to one another. Or
the object may be considered to be so placed with regard to a
vertical or horizontal plane.

This is best illustrated by supposing a cube to be so placed with
regard to a plane that the three lines forming one of its solid
angles, or points, are equally inclined to the plane, as also the
three planes containing the solid right angle.

The projections of the six edges of the cube will evidently be
equal to another, and the right angles veill be projected as angles
of 120° and 60°. Each face will be projected as a rhombus.
The longer diagonals being parallel to the plane of projection will
be of their original dimension.

Fig,Z,

Oftp 'bo -paxfc 32 .

Dvonmy

JVa/L.

Elsntiiorv.

Oflp: tofXUfS 33.

G. D. l>L.iO.

Fi^.^

y /

>^ i

y :

-- \

SodUf 43

lHg.6.

Ijumgirio VSmf.

.)«a||mA«14 ZSJMVwd S* C<nr«]ilGM(l«.

PRACTICAL SOLID GEOMETRY. 33

Draw a square, A B D (Fig. 1, PI. 10), Join the dingonal
A B. From each extremity A and B of the diagonal draw lines
making with it on each side angles of 30^. Let these lines meet
in the points c and d respectively, llien the rhombus A c B </
will be the square A, C, B, D isometrically projected, its angles
being 1?0 and SO.

Then AC : A c :: sin 120^ : sin 45^

i/3 : i/2

that is, the isometric projection of a line is to its true length as

To construct an isometric scale (Fig. 2) two lines must there-
fore be drawn in this relation. Take any line, say one inch, erect
at one end a perpendicular of the same length, and join the ends ;

the hypothenuse will represent V 2. Set off this latter length
along the original line from the foot of the perpendicular, and join
it with its other extremity. This hypothenuse will represent
V^ 3. Two lines are thus obtained in the required relation, and

if the scale of the drawing be set off along the line v/ 3, and per-
pendiculars dropped from its divisions to the other, an isometric
scale will be obtained.

The isometric projection of a circle will be the ellipse inscribed
in the rhombus, which is the projection of the square described
about the circle.

Let A C B D (Fig. 3), as before, be a square, and A c B </ its
isometric projection, A B being the diagonal parallel to the plane
of projection, join the other diagonal C D of the square meeting
A B in O. It is evident that the major axis of the ellipse will Ire
in the diagonal A B, and will be equal to the diameter of the
eircle (or side of square). Mark off on each side of the centre O
to Q and B* the semi-diameter of the circle. Q R will be the
major axis. Draw through its extremity Q or R a line paraUel
to the side of the rhombus meeting the other axis in T. O T
will be the minor axes, with which the ellipse can be described,
touching the sides of the rhombus at their centres S, S, &e.

The numerical ratios of the axis of the ellipse to the side of the
rhombus can be determined as follows : —

Since the angle Q T 0=60^ _

OT :0Q :: 1 : i/ 3

and as in the ellipse the sum of the squares of any conjugate
diameters are equal to the sum of the squares of the major and
minor axes.

Calling O T, 1,

4+ 12 = 8 0_S*= 16

O S2 = 2 ._

8= ^2_ _

.-. OT : OS : OQ :: 1 : ^2 : -v/3

Therefore any one of these dimensions being known, the others
can be measured from the isometric scale above described.

OEOMETRIOAL DRAWING.

Practical role
for drawing
the projection.

Nature of

perspective

projection.

In beginning an isometric drawing, draw first a vertical line on
the paper, and at any point in it two other lines, one on each side,
making angles of 120 with it. These three lines will be the iso-
metric axes corresponding to the three edges of a cube assumed
with its diagonal at right angles to the plane of projection. The
various dimensions of the object to be represented can then be set
off on the three isometric axes, or lines parallel to them, from the
isometric scale, provided that they are dimensions parallel in the
object to the three planes forming the solid right angle.

The isometric projection may be either considered, a plan or an
elevation, and in most cases will convey a better idea of the relative
positions of the different parts of the object than would be given
by separate plans and elevations. It has the appearance of a
perspective view, though strictly an orthographic projection.

All dimensions parallel, but not otherwise, to the isometric ases
can be measured by means of the isometric scale, hence this pro-
jection is generally used only for the representation of objects the
principal planes of which are mutually perpendicular.

In Fig. 4, PI. 10, is shown the isometric projection of a door-
way, of which Figs. 5 and 6 are respectively the plan and front
elevation.

Perspective Projection.

67. The discovery of most of the rules of perspective projection
is due to Italian artists, and geometricians of the Renaissance
period, but Dr. Brook Taylor in 1715 first reduced the various
methods to a complete system, of general application, to planes
inclined in any direction to the picture plane or plane of
projection.

Perspective projection differs from orthographic projection in
that the visual rays from all points of an object to be represented,
instead of proceeding mutually parallel, converge to a vertex or
point representing the eye of the spectator.

If a plane be interposed between the vertex and the object,
the intersections of the projectors or visual rays with this plane
will give points corresponding to those of the original object.

If these intersections on the interposed plane be connected
similarly to the original points of the object, the resulting figure
is a perspective projection of the original object. Thus it appears
that the orthographic projection of any object is the section of
a prism or cylinder of projectors, whereas the perspective pro-
jection of the same object is the section of a pyramid or cone of
projectors. The constructions involved in the solution of a problem
in perspective projection are necessarily, therefore, more com-
plicated than those required for orthographic projection;

In these constructions many lines and planes are used, to which
it is necessary for the sake of distinction to give special names.
More than one= name has been given by writers to one and the
same plane, line, or point. In the following explanations those
-names will be selected which best define the science geometri-
cally ; the alternative terms, which are those usually employed by

PBAOnOAIi SOLID OEOMETBT. 35

writers treating perspective projection as a branch of pictorial
arty being entered in brackets after the more purely geometrical
term.

68. The preceding remarks may be illustrated by a reference Dcfinitioiif.
to Fig. 1, P]. 11; which represents a solid ABD standing on a
horizontal plane HOB and projected orthographically in the
figure fl' h' df and perspectively in the figure a /9 9 on the
vertical plane W Z X Y, interposed between the original object
and the vertex, or point of convergence of the projectors, V.

The plane HOR on which the object rests is called an original Original plane
plane. The interposed plane is the plane of projection (picture ^j^"n
plane).

It is best in the first instance to assume the planes HOR and
W2jYX as respectively horizontal and vertical, this inter-relation
being at once the simplest, and satisfying the most usual conditions
of perspective drawing ; but the principles and definitions which
follow are equally applicable when the planes are inclined, and
when the angle they contain is not a right angle.

The point on which the projectors convei^e is the vertex Vertex,
(position of eye).

The visual lines converging on the vertex are the projectors Pwjectors.
(rays).

A plane through the vertex parallel to the original plane is the Vanishing
vanishing plane of that original plane. ^ ^

A plane through the vertex parallel to the plane of projection Pa«Uel pl«n«-
is the parallel plane (directing plane).

A plane passing through the vertex and any line in space is Projecting
the projecting plane of that line, and the line is termed an Elf^niTKiie.
original line

The intersection of a projecting plane with the plane of pro- P^fpective
jection gives the perspective projection (picture) of the original P'^^*^ ®°'
line ; and the intersection of a projecting plane with the parallel I^irector.
plane gives the director of the original line.

The intersection of the projecting plane with the vanishing Radial,
plane of the original plane is termed the radial of the originfu
Hue.

From the above definitions it is evident that an original line^
(considered in that portion of it that lies between the plane of
projection and the parallel plane^) its radial, its perspective
projection, and its director, form a parallelogram.

The intersection of the original plane with the plane of pro- Trace,
jection is called the trace (ground line) ; and the intersection of
the original plane with the parallel plane is called the directing Directing line.
line of the original plane.

The intersection of the vanishing plane w ith the plane of Vanishing
projection is termed the vanishing line. ^"*®'

The intersection of the vanishing plane with the parallel plane ParaUelof the
is called the parallel of the vertex, vertex.

It is evident that this line is parallel to the trace and vanishing
line of the original plane.

GEOMETRICAL DBAWIXG.

Trace and
directing point.

Vanishing
point.

Axiom 1.

Axiom 2.

Axiom 3.
Axiom 4.

Axiom 5.

Axiom 6.

Axiom 7

The points in which an original line intersects the plane of
projection and the parallel plane are called respectively its trace
(seat) and directing point.

These points are respectively on the trace and directing line of
the original plane.

The point in which the plane of projection is intersected by
the radial of an original line is called the vanishing point of that
line.

This point is evidently on the vanishing line of the original
plane.

It is perhaps advisable to explun how the intersection of the
radial of a line wiih. theplane of projection has come to be called
the vanishing point. The perspective projection of a line in space
being the linte joining the perspective projections of various suc-
cessive points in the original line, such projected points being
given by intersections of projectors from the vertex to the ori^^cd
points, it follows, since the radial is drawn through the vertex
parallel to the original line that the intersection of the radial with
the plane of projection is the point on that plane given by the
projector to a point in the original line at an infinite distance
from the vertex, t.«., a point where the original line tends to vanish
or terminate ; that is to say, the whole perspective projection of any
original line, considered infinite on the further side of the plane
of projection, must lie between the trace of the line and its vanishing
point, obtained by drawing a line through the vertex parallel to the
original line.

The 'radials of all lines Ipng in any svstem of parallel planes
being all found in one vanishing plane drawn through the vertex
parallel to those original planes, the intersections of these radials
with the plane of projection will all evidently lie in the intersection
of the vanishing plane with the plane of projection ; that is to say,
the vanishing points of all lines lying in any system of paralld
planes will be found in the vanishing line of the parallel original
planes.

69. From a consideration of these definitions we derive the
following axioms, or general principles, on which depend the
various practical operations involved in making a perspective
drawing from given data.

The perspective projection of any original line lies between
its trace and its vanishing point.

Any system of parallel original lines, whether in one or different
planes, has a common radial

The projections of such a system of parallel original lines there-
fore have a common vanishing point.

The radials of all lines lying in any one original plane lie in
the vanishing plane of that original plane, consequently the
vanishing points of all these lines lie in the vanishing line of that
plane.

All parallel planes having a common vanishing plane, the
vanishing points of all lines lying in any system of parallel planes
must be found in the common vanishino^ line.

The projection of a line parallel to the plane of projection must
be parallel to the original line and to the trace and vanishing
line of thjB original plane in which it lies.

The projection of a plane figure situated in a plane parallel to

FRAGTIGAL SOLID GEOMETRY. 37

be plane of projection must be a figure similar to the original

-igure, but unlike the orthographic projection under similar con-

iitions^ the perspectively projected figure bears a ratio to the

>riginal figure depending on their relative distances from the

vertex.

Evidently the pTojected area is to the original area in the dupli-
cate ratio of the aistances from the vertex of the plane of projection
and the original plane.

Although the above axioms may be said to comprise the
whole of the preliminary principles of perspective projection, it is
necessary to call attention to one or two lines and points in con-
nexion with any given j^erspective projection, which are specially
important.

Of all radial s the line drawn from the vertex perpendicular to Distance of
^ the vanishing line or plane of projection is the principal, as it ^^ vertex-
fixes a much used vanishing point. This radial is termed the
distance of the vertex (distance of the picture) ; and the resulting
\ vanishing point is called the centre of the plane of projection,

(Point of sight, or centre of the picture.) Centre of the

This line and point are evidently respectively the radial and P^« of pro-
vanishing point of all original lines perpendicular to the plane of J^tion.
projection. Again, all planes perpendicular to the plane of pro-
jection have evidently the centre of the plane of projection as a
point common to their vanishing lines. Any two such vanishing
lines evidently also contain an angle equal to that contained by
the planes to which they relate.

Another vanishing point of importance in the construction of ^^mx, of
perspective drawings is that given by the radial to horizontal ^***"*^*
lines lying in parallel original pLines but inclined to the plane
of projection at 45°. This vanishing point is called the point of
distance.

This point is readily fixed on the ^-anishing line of bx\j original
plane hy laying off from the centre of the plane of projection on
either side a distance equal to the distance of the vertex. All
horizontal lines inclined at 45° to the plane of projection will
have their projections directed to one or other of these vanishing
points.

\ I

These general definitions and axioms may be illustrated by
Pig. 2, PL 11. In this figure HOR is an original plane at right
angles to V'XY a plane of projection. VP^ Pj is the vanishing
plane through the vertex V. The lines XY and Pi Pj are re-
spectively the trace and vanishing line of the original plane.
VQ lying in the vanishing plane is the distance of the vertex, and
j!^ this line is at right angles to the vanishing line. If A B C D be
a parallelogram lying in the original plane, II KK are the traces
of its sides ; VPj VPg lying in the vanishing plane parallel to its
sides, are the radials of those sides, and P^ P2 are the vanishing
points; IPi and KP2 are the indefinite perspective projections of
those sides, and consequently abed will be the perspective
projection, of the parallelogram.

70. To represent all the necessary operations on the plane of Practical
the paper vrhen making a drawing, the original and vanishing pj™*^^"^ ^"

38 OEOMETBIOAL D&A.WIKO.

planes may be supposed to turn round on the trace XY^ and the
vanishing line Pi Pg preserving their parallelism till they coin-
cide with the plane of projection. The parallelogram would
assume the position A^ B' C^ D' on the plane of projection, but
the positions of II, KK, P^ Pg would not be affected, and the
same perspective projection abed will be obtained as before by
drawing IP^, KPg. The new position of the vertex V will be
V, V'Q being evidently equal to VQ.
A first method, pjg^ 3^ pj^ H^ represents these operations performed on the

plane of the paper in drawing the perspective projection abed
of a square A B C D. It is not necessary, nor always possible,
to draw the original plan A B C D. It is sufficient to fix its posi-
tion on the plane of projection by giving the trace of one side, the
angle this side makes with the trace of the original plane, the
distance from the trace of the side of one of the angles of the
square, and the side of the square. For let I be given as the
trace of one side CD, inclined to the plane of projection at an
angle d®, then if VPi be drawn from V to make an angle B° with
WZ, the parallel of the vertex, P^ in the vanishing line will be
the vanishing point of CD, and the side of the square parallel to
it. IPi wiU therefore be the indefinite perspective projection of
CD ; let the distances IC and ID be known ; make 1$ I7 equal
to these distances, and P^ v' in the vjanishing line equal to Pi V
the radial ; then lines drawn from h and 7 to r will cut IPi in c
and d the projections of C and D. .

This construction depends on a principle which is of constant
application in perspective projection^ and may be thus explained.
If two Hues lA PV (Fig. 4, PL 11), paraUel to each otlier, and of
any lengths, he drawn from the extremities IP of a fini-te line, and
AV he joined, cutting IP in a, then if lA VF he suppo scd turned
round into any other position, lA' PV, provided they retain their
parallelism and length, the line A' V joming their extremities in
the new position w£& still pass through a. For it is obvious that
IP must be in the intersection of the planes of the two positionSj
and therefore a line common to both planes. The triangles of the
positions being similar, and one side and two angles of either
triangle remaining the same, the third side will remain constant.

The same construction would have held good had lA and IB
been brought on to the trace line XY (Fig. 3, PL 11).

The figure may be completed by joining KK, the traces of
AD, and OB, with Pg their vanishing point ; but in the event
of these lines not falling within the limits of the paper, the
point b can be fixed by dm wing the diagonal BD of the square,
obtaining its trace on the trace line and its vanishing point Ps^
and joining these two points by a line intersecting the indefinite
projection IPi of AB in the point b. A line through b directed
on Pg and produced backwards would proceed to the trace K*
&lling out of the limits of the drawing, and would give the
point e on IPj the indefinite projection of DO.
A second One or two other conventional methods of making a projection

method. fyQ^ a gj^gjj^ pl^^jj gjg shown in Figs. 1 and 2, PL 12.

In the first (Fig. 1) the plan A B D of a cube is placed
above the line Pi Pg, which line with reference to the plan

Fuf.l.

-.€

y r

Opfi.Uf jxic/e SS .

PRAOTIGAL SOLID QEOMETBT. 39

le horizontal trace of the plane of projection. The points
re the projectons from the angles of the solid to the vertex V
"sect the plane of projection, when brought down to the line
r^ will give lines as bV^ cc\ dd\ &o., on which will be found
projections of the vertical edges of the solid. The vanishing
ito Pi Pg are obtained as usual by the radials VP^ VP, drawn
iLlel to the original lines A B, C Dj and A D, B C res-
tively. Lines drawn to these vanishing points from the traces
the sides brought down to the line X Y will give the
T upective projections of the sides of the base a! V d d\ and the
)er face of the cube will be obtained by placing the height
' Jthe cube on the lines jS jS $^ &c., and drawing lines to the
>per vanishing point, jS $, &c. being the traces of the sides
B, A D, &c.

In this method the line P Ps plays a double part ; in the first
,^'itance it represents, as already stated, the horizontal trace of the
ue of projection; in the second instance it represents the
rtical trace of the horizontal vanishing plane> or in other words
e vanishing line^ while X Y becomes the vertical trace of the
j^lginal plane^ or in other words the trace or ground line.
I Fig. 2 represents yet another method where for convenience A thiid
jke the plan of the solid is placed below the line X Y. In this method.
ise X Y and Pj P {d) represent respectively the trace of the
iginal plane^ and the vanishing line ; x y represents the position
% the horizontal trace of the plane of projection with regard to
^ solid A B C D E F. The solid represented is an irregular
jht pyramid^ Q being the centre of the plane of projection and
{d) the point of distance or the vanishii^ point for horizontal
fnes inclined to the trace of the plane of projection at 45^. The

joints ab cde o( the base are fixed by the intersections of lines

Idpresenting the horizontal traces, or intersections with the original

plane, of planes perpendicular to the original plane, but inclined to

/ ihe trace of that plane at 90° and 45°. The points Q and P (rf)

feing in the vanishing lines of these planes respectively are

lierefore the vanishing points of all horizontal lines in those

planes. Hence the points abcde ba well as the point where the

axis of the pyramid cuts the plane of the base are fixed as shown

in the figure. The height of the figure is obtained in a manner

omilar to that employed for the cube in Fig. 1. This method of

■ -., employing the centre of the plane of projection and the point of

distance is one of great utility in perspective projection, and it is

frequently employed in cases where it would be inconvenient to

show on the drawing the actual position of the vertex and obtain

from that point the various vanishing points required.

The same method has been employed in Fig. 3, which represents
the projections of two equal circles in different positions.

71. The perspective projection of any curve can be drawn as in ^'^^^^ ^^®^'
''">. orthographic projection by taking the projections of a sufficient
' numiber of points in the curve and connecting them. It is

suiBcient, however, for our purposes to consider only the circle.

The perspective projection of a circle must evidently always be a

GEOMETBIOAL DRAWING.

Oircle.

General
remarks.

Vanishing
points of lines
inclined to
horizontal
plane.

conic section. For the projector of all points of the original
curve haying the vertex as an apex must form a conical surface
and the section of this surface made by the plane of projection
must be a conic section, and the perspective projection of the
original curve. If the plane of ^projection lies between the vertex
and the original circle the perspective projection is an ellipse or
circle ; if the original circle touches the directing line, the plane of
projection would necessarily be parallel to a side of the projecting
cone, and the section of the cone would be a parabola ; if the
circle cut the directing line, the section being parallel to the axi^
of the cone would be a hyperbola ; and lastly, it will be evident
that in certain positions of the original circle the perspective pro-
jection may be a straight line.

In drawing the perspective projection of a circle, it is UB.ially
sufficient to fix the points given on the original curve by the
inscribed and circumscribed squares, as shown in Fig. 3, PI. 12.

In this figure XY represents the trace of the original plane
QP(c?) the vanishing line. One side of each of the two circum-
scribing squares represented, has for facility of construction been
assumed coincident with XY. P (rf), the point of distance, thus
becomes the vanishing point of the diagonals of the circumscribing
squares, he point Q being the vanishing point for those sides
of the squares at right angles to XY. Hence the fourth sides
of the squares b c can be readily drawn, as also the projections
of the diameters parallel to the sides, thus determining the point
of contact, and \i ad or h c be divided in K H as the side of
the inscribed square, we obtain the points kik I on the diagonals
through which the projection of the circle must be drawn.
It will be noticed that e the intersection of the diagonals is not
the centre of the ellipse. For methods of finding the true centre
of the ellipse we must refer the reader to larger works in which
the matter is treated at length.

72. It will be evident from a consideration of what has been
already explained that the whole of the art of perspective drawing
may be condensed into one operation, viz., that of, finding the
perspective projection of a point, for all solids are bounded by
lines which contain points, the projections of which being fixed
the projection of the solid is fixed. When, however, points to be
put in perspective are numerous, and when (as is mostly the case
in practice) they have certain given relations to one another,
the constructive method of finding vanishing points, to which
may be directed lines containing projections of many of the
given original points, will very much facilitate the projection of a
figure composed of many related parts.

Principles have been given, and methods shown, -for finding
the vanishing points for all lines which are horizontal, and it only
remains, to cover all cases, to show how to determine the vanishing
points, and the resulting perspective projections of lines inclined
in any direction. To facilitate reference the rule for finding the
vanishing points of such inclined lines may be. stated as an axiom

PBA.OTICAI. SOLID GKOHETHr. 41

inea not horizontal, whether ascending or deaoending with Axiom 8.

X reooe to an originnl horizontal plane, have their Tanishing

' ttB in the vanishing lines of the verUcal planes containing

n ; those ascending finding their vaniehing points above, ana

le descending below the vanishing line of Uie original hori-

tal plane to whidi the; reFer.

\ riuB axiom will be easily understood if we suppose a vertical I

« oe to be passed through the oiiginal inclined line> and a plane

Vllel to this plane drawn through the vertex. See Fig. 1,

13, in which WZXY is the plane of projection, HOR is the

giinal horizontal plane with trace XY, VPPi b the vanishiDg

ne to this original plane, PP, being the vani^ing line; AB is

original inclined line inclined at 6° to the horizontal plane,

s. ■ being its plan and VP being the radial of a b. Now if parallel

^ttical planes MZ^ and WNV be passed through the line A B

.^ d the point V respectively, the interseclions of these planes

th the plane of projection will evidently be vertical lines kZ

^ d WP, passing through the trace k, and vanishing point F, of the

m ab. Now the plane MZA may be supposed to be an original

toe, its trace being kZ, and as the plane WNV is parallel to it

rough the vertex V, WP is its vanishing line. Therefore, by

'^ . joai 4, the vanishing points of all lines lying in plane MZi will

"^i fonnd in WP indefinitely produced. From V in plane WNV

|aw a line parallel to AB, meeting WP in p ; then Wp is the

dial of AB and p is the vaniahing point of AB, and evidently

f is its trace ; therefore Kp represents the indefinite perspective
fojection of AB on the plane of projection WZXY, a! b' being
■ ie projection of the length AB. Again, it is evident that the
^ Bgle contained by VP and V/> is equal to that contained by
ke original line AB, and its plan a h, if these lines are produced
■ intei'sect, and is equal to the angle of inclination of AB to the
riginnl horizontal plane HOR. Hence to find the point p on
ite line WP we should only have to suppose the triangle j'PV
pieeled round on WP into the plane of projection.
j The practical method, therefore, of finding the vanishing point
f nny inclined line may be thus stated.

! Through the vanishing point of the plan of the line draw a
terticsl line. From this vnoishing point also set off along the
famishing line a distance equal to uie radial of the plan (aa from
^P to P|). From the point thus obtained draw upwards or
lown^vards, according to the inclination of the original line, a line
baking an angle equal to that at which the original hne is inclined,
rhen the intersection of this last line with the vertical line drawn
Hirough the vanishing pointof theplnnof the original inclined line,
will give the vanishing point required.

' Fig. 2, PI. 13, showa the perspective projection of a box in Ocnanl
' drawing which these general rules have been applied. The plane *^5^^^„
Bf projection has been assumed coincident with the front of the box, ^^Sing ^
»nd tiie projeolJon of the top, bottom, and interior of the body of penpeiitlTe
the box have been fixed by the use of the centre of the plane of pro- p«u««wb-
Section Qand the point of distance P (rf), which have teen employed

4394S. •*

42 GEOMETBIGAL DBAWIHG.

throughout as vaniBhing points. It remainB only to fix the
yaniehing points for the lid of the box, which hafl here been
assuDled to have the front and rear faces inclined at 75° to the top
of the box when closed, while the two side &ceB are formed by
vertical planes. The lid is also supposed to have been opened
through an arc of 30°. By drawing the perspective projection of
the original semicircle of revolution and finding the vanishing
point ?2 on the vertical line PjQ, passing through Q, the
vanishing point of the plan of AB, (which is done by drawing a
line from P(rf) making an angle of 30° with QP(d)> ^^^ finding
P2 the intersection of this line with QPg,) for the line AB and
lines parallel to it we can through a draw ab directed on Pj
and fix the point b on the curve. In a similar manner c and d
can be fixed by drawing from b and a lines directed on Pj and Pj
(not shown for want of space), the vanishing points for the
lines BC and AD and lines parallel to them, and fixing these
points on the perspective projections of their curves of revolu-
tion. Or, and this would give a more accurate result in a drawing
to so small a scale, one of these points as c may be fixed by
passing a vertical plane inclined at 45° to the plane of projection,
and finding where in c the line be intersected it, and by then
drawing from c a line directed on the vanishing point Pj and
fixing d by the intersection of this line with ad. Or, if it were
preferred, all the three points, S, c, d, might be fixed by passing
vertical planes inclined at 45° to the plane of projection through
B, C, and D. Having got one end of the top of the box, the other
end being in a parallel plane presents no difficulties in drawing
and the solid can be completed.

General 73. A few general remarks on the method of disposing the

remarks on plane of projection and vanishing points, and other matters con-
planTorpro- Dccted with the making of perspective drawings, may not be out of

jection, vertex, place.

^*^t^^ The aim of perspective drawings is to furnish pictures like

' ^' those the objects would themselves present to the. eye of a
spectator. Geometrical perspective assumes that the eye of the
spectator may be placed in any desired position with regard to
the object viewed, and that it is capable of viewing the whole of
the object whatever the angles of sight, horizontal or vertical,
within the limits of which the object faUs. But, in fact, the eye of
man is not adapted, without alteration of the direction of its axis,
to embrace a larger angular field than that contained within 50^
to 60° horizontally, and 40° vertically. Although, therefore, the
perspective views of any object on piu'ely geometrical assumptions
are absolutely correct, it is advisable, to avoid apparent distortions
in making perspective drawings, to limit the field of view to the
angles stated above.

Shadows It is not proposed to go int6 the question of shadows, though

the introduction of these into any perspective representation tends
much to heighten the efiect and add to the clearness of the
drawing. In most ordinary cases (the sun being a^umed as the

PBAGTfOAL SOLID GEOlfETBT. 43

luminary) perspective shadows may be obtdned from the ortho-
graphic projections of shadow thrown by an object, under given
conditions of direction of light, on planes receiving shadow.

Problems relating to Irregular Ground and Defiladem

74. In drawings prepared for the design of works of fortification,
irregular ground is represented in plan by a series of horizontal
contours (para. 35) occurring usually at regular vertical intervals,
the datum plane being either the mean sea levels or a special plane
for each plan, assumed at some convenient leveL

The various problems connected with the planes of fire and
defilade, the intersections of these planes, and of others related to
them^ with the ground and each other, can be worked out with
the aid of these ground contours by methods similar to those
already treated of in the preceding parts of this chapter. For
example, the intersections of regular planes, such as those of a *]

glacis, or those of a cutting or embankment, with irregular ground, <

may be determined by the use of Prob. 5 of solid geometry ; or, I

again, the representation of a road, which shall pass across the
surface of irregular ground under certain conditions of gradient, is
drawn by the method illustrated by Prob. 1. Such instances do
not call for any detailed explanation. The following problems,
however, which are of constant use in the defilading and designing
of works, may be noticed at greater length.

75. To determine a plane containing a given straight line, and Pbobum l.
tangential to ground given by its contours.

Let ab (Fig. 1, PL 14) be the line, a being the lower point.
Determine in a A points which have the same indices as the
contours of the ground, and from each such point draw a tangent
to the correspondingly figured contour. Then the tangent which
makes with a b towards a the smallest angle will be a horizontal i

of the required plane.

It is evident in the first place that the planes of which the
tangents to the contours are the horizontals must, in touching the
ground, come in contact with it at the points where these
horizontals touch contours of the same index. ,'

In the next place, to show that it is the tangent which makes
the smallest angle towards the lowest part of tiie line that fixes
the tangent plane, let it be assiuned, first, that the relative posi-
tions of the given line and surface are such that the required
plane must rise from the line towards the surface.* The steepest
of the planes whose horizontals are drawn tangent to the ground
contours, will be the tangent plane, for any plane of less inclina-
tion would cut the ground. And that plane which is steepest in
this case is given by the horizontal which makes the smallest
acute angle with the lower part of the line.

* The plane rises or falls from the line to the surface according as a normal to
the horizontals, drawn irom the lowest point of the line, lies nearer to or farther
ftom the muiace than the Une itself.

D 2

♦.

OEOMETRIOAL DSAWIKG.

Problem 3.

Pboblbx S.

Problem 4.

Next, if the relative poeitions of the ^ound and line are such
that the required plane mugt descend firom the line, then, by
reasoning analogous to that in the first case, the tangent plane
must be the plane of least inclination, and that tangent horizontal
which makes the greatest acute angle with the upper part of the
line, will manifestly give this plane ; that is to say, in either case,
the horizontal which makes the least angle with the lower part of
the line is the one which fixes the tangent plane.

When the given line is horizontal, tangents parallel to it should
be drawn to each contour and that tangent horizontal, which, in
the case of planes ascending from the line, gives the steepest plane,
or which, in the case of descending planes, gives the plane of least
inclination, fixes in each case the tangent plane.

76. To draw from a given point lines to touch a given irregular
surfoce.

Let tlie several lines be drawn in plan across the contours of
Ihe given surface. From the given point (p. Fig. 2) draw a line
ill any direction, and graduate this line from the given point in a
manner similar to the contours of the ground. Taking each
secant line in succession, join the points of its intersection with
the contours to the corresponding points on the assumed graduated
line. By reasoning similar to that in the last problem, the line of
junction which makes the least angle with the lower part of the
graduated line determines the point of contact of the secant line
with the surface. Using this point and the original given point,
the secant line can be graduated so as to be in contact with the
ground. This problem may be employed for tracing the limit of
vision or fire from a given point.

77. Throu;i;h a given point to draw a plane touching a ^ven
irregular surface.

This problem evidently admits of many solutions ; that plsQ^
(or planes) should be selected which best answers the purposes of
the design. The working out of this problem is similar to that
of the last problem. A number of secant lines are drawn from
the given point through the most prominent salients or ridges
and the re-entering angles or hoUows of the ground, their tangent
points with tiie ground, found by the last problem, and the
lilies graduated accordingly. Taking points of the same index on
each graduated line (in Fig. 2 the points at the level 30 have been
taken), join these points, forming a horizontal section of the solid
angles of the planes contained by the tangent lines. This
definition of the solid angle enables us to measure the inclination
of the planes containing any two of the tangent lines, and of
these planes that which best fulfils the conditions and purpose of
the design is to be taken.

78. Through a given point to draw a plane touching two
prominences.

Through the given point (p, Fig. 3) draw any line between the
prominences and graduate it similarly to the ground, so that it
may be as nearly as possible in the required tangent plane*
Draw from the points of division on the line tangents to tb^

CO. PL. 14

'Mi4(.p[idi.22.B«i!fotd S^ Cyn-ulGaxiBi.

Oppto-p€M£fe44.

PRACTICAL SOLID OEOMETRT. 46

correspondingly figured contours of each prominence^ and find
the tangent planes to each prominence by problem 1. It is
evident, if these planes were one, that their horizontals would be
parallel; and give parallel and equal scales. If this is not the
case, other trial lines must be drawn from the given point, or the
line first drawn must be again graduated and the process repeated
till the horizontals become pandleL

79. To determine the most conunanding point with regard to a FaoBtni s.
given fixed point, and within given limits of distance.

'Phis may be done by drawmg a line to what appears to be the
most commanding point, and using this line as the generatrix of a
cone whose vertex is the given fixed point A comparison of the
depths of intersection of this cone with other parts of the sur-
rounding ground within the given limits will at once show the
exact position of the most commanding point. Planes may then
be drawn by problem 1, to contain the line joining the most com-
manding point with the vertex point, and to touch the ground on
either side of it, or, in the event of these planes forming a valley
towards the vertex point, a single tangent plane may be obtained
by problem 4, if such a plane would be more suitable to the con- |

ditions of the defilade of the work. If the work is to be defiladed
by portions the same process may be repeated to determine the
most commanding points (or points of danger)^ as regards each

portioil, or these points may be obtained by a comparison of the i

contours of the cone originally eniployed with those of the ground.

80. In considering the defilade of a work, by which term is Geneiml
understood the arrangement of the interior of a work so that it be
at the least concealed from the view of the enemy, the whole of the
exterior space from which a work is to be defiladed being marked
out, the commanding points within the limits should be ascertained,
and the plane, or planes, of defilade for the whole work, or for
the work considered in sections, should be drawn, and the work
designed in the manner that appears most suitable. It is usual
to assume that the planes of defilade should pnss at least the
height of a man's shoulder above the commanding points to which
they refer. It then remains to design the work so that as far as
possible the whole of the interior space may be concealed from
view, and the terrepleins protected from the effects of reverse and
enfilade, as well as of frontal fire. To effect these objects, the
crest lines may be raisedt the terrepleins lowered, and parados
and traverses constructed ; or any advantageous combinations
of these methods may be adopted in one and the same work, or
part of a work. Generally speaking, any face of a work com-
manded by ground in front, in rear, or in its prolongation, may
be defiladed from the first by arrangement of terreplein, from
the second, by the use of traverses or parados, or by placing
it in or below the plane of defilade of some other face between
it and the point of danger, from the third (unless the face under
consideration is short) by traverses dividing the face into short
portions.

ELEUBMTABT FXBLD TOBTHIOATION.

CHAPTER II.

ELEMENTARY FIELD PORTIPIOATION.

General prin-
ciples.

Influence of
ground.

Classification
of requisites of
defence.

Fire effect.

Movement.

Active and

pasnve

defence.

Section I. — Intboductobt.

81. The advantage sought to he obtained by standing on the
defensive, and receiving the attack of the enemy in a chosen
position, is the infliction of severe loss on him by the fire of
troops posted in such a manner as to see him at every step of his
advance, whilst themselves more or less protected from his fire,
and hidden from his view ; so that finally he will be forced to
retire from sheer loss or demoralisation, or the defenders will be
enabled to close with him on more equal or even superior terms.

To help^ to bring about this result the enemy is subjected to
every possible hindrance, both from the nature of the ground he
has to cross (steep, rough, or swampy), and from artificial ob-
stacles placed in his way for the purpose of detaining him under
fire, or limiting his movements to ground favourable to the
defenders.

At the same time, every provision is made for the free move-
ment of the defenders throughout their own position, and over
those parts of the ground in front where they may desire to meet
the enemy.

These advantages must be looked for chiefly in the selection of
suitable ground, and in a proper disposition of the troops on iti
but a great deal can be done by art to increase them, or to supply
them where they do not exist, and this is what is understood by
the term field fortification.

The requisites of defence, as above_ described, may be shortly
classified as follows: —

Fire effect : —

1. Exposure of the enemy to defenders' fire.

2. Cover for the defender from enemy's fire.
Movement : —

1. Difficulty of movement for the enemy. (Obstacles.)

2. Freedom of movement for defenders. (Communications.)
The defence may be either of an active or passive character.
An active defence implies that the defending force is strong

enough (whether from numbers or morale) to attack the enemy
in its turn, having first promoted this object by exposing Ws
force to severe fire on a chosen vantage ground. In this case, Jn
addition to fire effect, perfect freedom of movement is required on
the ground over which the counter attack will be made.

A passive defence must be resorted to in cases where it is merely
intended to stop or delay the enemy, and where, from inferiority
of numbers or' other considerations, the idea of counter attack can-
not be entertained. In this case, m addition to fire effect^ the
greatest possible amount of obstacle to the enemy's movement

UVTBODUOIOBT. 47

should be made, in order to increase the effects of fire, and avoid
personal collision. In active defence, the existence everywhere
of such impediments would interfere with the subsequent advance
of the defenders.

In purely offensive movements field fortification finds a limited FieM fortUie*.
use in ooabling what has been won to be held by small numbers, ^^ ^.° ^^
and in guarding agamst possible reverse.

The time available for works of field fortification is usually Inflocnoe of
short> and the labour of the troops themselves is all that can be ^^ ^^*
reckoned on under ordinary circumstances; the supply of tools
that an army can carry in the field is, moreover, limited. Hence,
how much work to do^ and where to do it, is the important question,
depending not only on the ground itself, the working parties, time,
and tools at disposal, but also on the character of the defence
Inquired from the troops.

The slight and simple works that can be undertaken when there
are only a few hours for preparation, or even in the actual presence
of the enemy, may be conv^ently treated separately as hasty
defences. They are not limited, however, to such cases, but are
usually combined also with the more considerable works which
may be constructed when days or weeks are available, and which
are termed ^eZrf works. Both alike belong to Jield fortification ;
but outside of this there lies another class of works, constructed
beforehand in time of peace, to secure points of which the import-
ance in time of war can be foreseen. Works of this kind, though
based upon the same principles, differ widely in character from
works of field fortification ; years may be spent in their con-
struction, durable materials, such as iron and masonry, enter
largely into it, and they are classed as permanent fortification.

Ranges and Effects of Firearms.

82. The application of the principles of fortification depends so
much on the nature of the weapons employed for attack and de-
fence, that before going further it will be well to give some facts
respecting the kinds and effects of fire to be taken account of.

Of the losses in battle, according to the experience, of the last
two wars, in 1866 and 1870, 95 p. c. are due to firearms ; and of
these, 80 p. c. are due to infantry fire.

The Martini-Henry rifle will fire 25 unaimed or 12 aimed shots Rifle Bate of
in a minute. ^^'

The fire of individual marksmen is effective up to 1,000 yards ;
but 600 yards is usually considered as the limit for the indepen-
dent fire of troops in the main shooting line.

Anything below 300 yards is considered close range, requirinnr
but little if any change of the rifle sights.

It will pierce about 12 in. of fir, about 5 in. of oak, about 0*3 in. Penetration,
of irony and penetrate nearly 2 feet into earth.

The Gatling gun ranges effectively up to 1,200 yards, and i§ Gattingganf.
capable of delivering a continuous stream of bullets at the rate of
about 400 per minute.

ELEMENTABT FISLD K>BTI110ATI0N.

Field guns.

Projectiles.
SheUs.

Shrapnel.
Case shot.

Eockets.

Direction.

Frontal.
Oblique.
Enfilade.

Its fire is equal to that of about 22 riflesi and nearly equal to
that of two 9-pr. guns up to 1,200 yards.

The Gatling gun as a weapon for defensive positions is of great
value. It is especially applicable for defending the passage of
bridges or defiles; for use in villages and at barricades; for
flanking fire, and for sweeping ground which has to be travened
by assaulting columns. It is at close ranges that the GhitUng
produces the greatest effect.

On ordinary fields of battle nothing heavier than the 16-pr.
R.M.L. gun is likely to be met with. Though artillery fire ranges
beyond 5^000 yards it is seldom worth while in the fidd to nuJ^e
uee of it beyond 3^000 yards.

Field guns can fire about two rounds a minute, being laid at
each round.

The projectiles usually fired from guns are common sbell, •
shrapnel shelly and case shot.

Common shells may be used with either time or percussion
fuzes, and are chiefly employed against artillery^ masses of troops,
or material objects, such as earth, wood, masonry, &c«, at all ranges
up to 3,000 yards.

The penetration of the shells of field guns into earthen parapets
at a range of 1,000 yards is from 4 to 10 feet, according to the
nature of the gun, and the character of the parapet. The penetra-
tion into sand is only two thirds of that into ordinary earth, and only
half of that into loam or clay. The bursting charge is about ^lb«
for a 9-pr., and lib. for a 16-pr.; and this charge acting as a
mine, about 2 ft. under the surface, will usually throw out about
half a cubic yard of earth per lb.

The penetration into brickwork is about 2 fit. ; into oak about
2ift.

Shrapnel shells can be employed at all ranges of the gun against
troops.

Case shot is employed on emergency against troops at short
ranges, viz., 100 to 300 yards. It can be fired at the rate of
three rounds a minute.

Eockets range with full effect from 400 to 1,200 yards ; carry
either shot or shell, and from their portability can often be used
where guns cannot.

They are useful against cavalry (the noise frightening tbe
horses) ; for incendiary purposes ; and in mountainous countries.

Different kinds of Fire,

83. Artillery fire, as to its direction with reference to the
horizontal plane, is said to be either front (or frontal)^ oblig^^*
erifilade, or reverse.

Front or frontal, when it strikes the front of an object perpen-
dicularly, or nearly so.

Oblique, when the object aimed at is struck in front, but not
perpendicularly.

Enfilade, when the fire is directed along a rampart or lioe of
troops.

OCEABING THE OROUKP. 49

Eeverse, when it strikes the parapet or line id rear. Revene.

Again, artillery fire as to its trajectory may be either direct, Tni^bUxj,
indirect (or curved), or high angle Jire.

Direct, from p:uns with service charges at all angles of elevation Dinet
not exceeding 1 5*.

Curved or indirect, from guns with reduced charges, and from Carved,
howitzers and mortars at all angles of elevation not exceeding
15°

High-angle fire, from guns, howitzers, and mortars, at all angles Htgh -s agi e
of elevation exceeding 15®, **••

Section 2. — CufiABiNG the Ground.

84. The selection of ground naturally free from obstructions Clearing tbe
and favourable to the efiect of the defender's fire is of the first '^vw***
importance, but .more or less clearing will almost always be
necessary.

This must be undertaken systematically by special parties, the
strength of which will depend usually on the supply of tools
available for this particular class of work.

Every effort should be made to clear the front up to the efiec- When to
tive range of rifles, particularly on those portions of the ground *^••'•
where it is thought the attacking line will make their principal
effort.

Again, it is most important to clear in front of those portions
of the ground which are especially arranged for passive defence.

Timber of all sorts is that which most often screens the advance,
and should be cleared.

Iledges which are paraUel to the frt)nt must be removed, unless Hedges. p

their front can be[swept by fire from another part of the line ; and ^

even under these circumstances if they are likely to interfere with f"

counter-attack they should be levelled. V.

Those that are perpendicular to the line may be left standing ^B

when within close rifle range (up to 300 yards), as they break up V

the attack into sections, and thus favour counter-attack, provided '.

they do not interfere with flanking fire or movement f

Hedges can be cut down by men at two-pace interval in from a(

6 to 18 minutes ; if very busby, a pole and ropes may be used to v\^

expose tbeir lower brancbes to the axe.

Two untrained soldios with axes', cut down trees of 4, 6, 9, 12, Trees. ^ ^'

and 18 inches diameter in about 1, 3, 5, 9, and 15 minutes respec- ' \

tively. Soft wood trees (when not more than 2 to 9 feet in >'

diameter) can be felled in 20 to 30 minutes by four men ; if of hard i

wood they may take three times as long. Large trees when felled ^'

must often be lopped so as to prevent their acting as cover on the p

ground. Detuls of the mode of felling trees, &c., will be found in
the chapter on Siege and Field Works. \

Timber felled in making clearings has often to be removed for
defensive use ; any wagons are convenient for carrying small trees
and brushwood, but for heavy logs devil-^arts are best.

Vhe artillery and all mounted trans|>ort branches of the service
carry a proportion of spare wheels and axles., others can be got
from oouniay carts, &c. ; poles can be fixed to these axles in an
hour or two, and the spare dragH^hains used as slings t working

SLEUEirrABT FIBLD FORTDTIOATIOK.

Walls.

Hollows.

Brashwood.
Hop-woods.

Tall grass,
com,- &c.

partiesy aided bj troop-honas with laaaoea, can, by means of devil-
carte thui improvised, handle timber mth ease.

The same principles as for clearing hedges apply to inralk.
They can be knocked down by a dozen or more men uaing a trunk
of a tree, or railway bar, as a ram. Low building may be simi-
larly treated ; if high, they must generally be blown down with
explosives.

The ruins must be levelled so as not to give cover.

Hollows can be filled with the debris of walls, &C; or better
still with abatis.

Troops at five paces apart clear 30 paces forward in bnuhwood
five or six years old in eight hours.

In felling hop-woods of 10 years growth* a woodman can clear
five paces by 36 paces in a day.

Occasionally, tall grass, com, or reeds may impede the defenders'
fire and view, and should be trampled down by men in line, or
cut down, or burnt.

Section 3. — Hasty Intbenghments.

Natural cover. 85. Oover ^ is required for all the troops within range of the

enemy's projectiles, for the shooting line as well as for the sup-
ports and reserves. Nearly all ^ound will naturally afford a
good deal of the necessary protection, if not in a form that can
be at once used, at any rate in a form that can be readily adapted
for use.

Supports and reserves, for instance, can be screened and shel-
tered behind undulations of the ground, woods, villages, embank-
ments, cuttings, &c., and men firing can be concealed behind
hedges, banks, walls, and in ditches, if these happen to be in the
right place ; but in most cases such natural cover will require
adapting to the exigencies of thecase.
Artificial cover. In providing cover, of whatever material, regard must always

be had to the projectiles expected to be encountered, the time for
construction, as well as the intended duration and character of the
defence, and whether active or passive. Where active defence is
intended, the cover must afford shelter from fire without hindering
the advance of any class of troops ; it should, therefore, either be
of slight form or provided with well-defined and wide exits. For
the passive defence, it should be as strong in profile as time and
means will permit.

Of all materials which can be employed for improvised
defences in the field, earth is the most useful, and generally
applicable.

It can be adapted by unskilled hands, and is the best obstruc-
tion to projectiles ; it can be used in combination with wood, iron,
brickwork or masonry, and in this way, according to the time
afforded for preparation, excellent cover and obstacle can be
obtained.

Wood requires special tools, and workmen more or less skillecl;
it will not resist artillery fire by itself, but is much used where

Materials.
Earth.

Wood.

SHELTBa TIt£N('IlES

HASTT INTSSNOHMBNTS. 51

infantry fire onlj is expected; also for supporting earthen
jstructures.

Brickwork or masonry is used when suitable walls^ houses, &c., Brickwork and
happen to be on the spot, but is rarely built specially for field "^•o'l'T'
fortificationa Walls will not as a rule resist field artillery.

Iron, on account of the difficulty of working it, can only be used Iron,
if found on the spot in a convenient form. Where railways exist,
great use can be made of the rails for the walls and roofs of
defensive structures.

Frequently cover which merely screens, though it does not resist Screens,
shot, is of service, such as paliues, &c.

During the cannonade, which is the preliminary of most en- Enemy's fire,
gagements in which guns take part, the defenders are under the
fire of shrapnel and other shells fired at long ranges ; when the
enemy's infantry closes their artillery fire must cease, and infantry
fire at short ranges takes its place.

For the shooting line, therefore, such cover is required as to
give good shelter from the distant fire of artillery and to admit
also of the free use of weapons from behind it. The cover must
also be capable of being obtained quickly, as time may be, and
often is, the ruling condition.

Shelter Trenches.

86. Earth cover is suitable alike to the most hasty and the Cover for
most deliberate fortifications. infentry in

A shallow trench of very small dimensions with the earth *<^*^®'*-
thrown to the front will very quickly afford cover to men lying in
it against artillery fire, and if the mound of earth be of suitable
height, the defenders can fire over it when required, whilst the
whole wiU present no obstacle to the advance of any troops over
it, should that be desired.

Small trenches of this class, called shelter trenches, arc diffi- Shelter
cult to capture by an attack in front when defended by steady trenches,
troops with breech-loaders. They form the bulk of the fortifica-
tions of ground prepared for active defence, and are also used
for the passive defence when time for preparation is short.

Experiments at Dartmoor in 1869 with 12-pr. shrapnel at 1,000
yards against targets representing a front . of 15 files, gave an
average of 11 hits per round. Supposing the men to have knelt,
these hits would have been reduced to J, and supposing them to
have been covered by shelter trenches, to about 2^.;

Fig. 1, PI. I.* shows a shelter pit for a single rifleman; the Shelter pit.
dimensions can be altered by each individual to suit himself.

* In the figures in the pla tes th e area of the sections of the ditches and parapets

in square feet is shown thus, | 18

The number of cubic feet in a task is shown thus, (m).

All h^hts above ground level are marked with a plus sign ( + ), and those
below with a minus sign ( 7- ).

ELEMENTARY FIELD FOBTIFICATION

Shelter trenclu

Modification of

musketry

trenehes.

Cover for
men's heads.

Log loopholes.

Sandbag loop-
holes.

Brushwood
loopholes.

Fig9. 2 to 4 are the ordinary shelter trenches, the drill for which
is described in the '' Field Exercise/' All of these trenches can
be passed by infantry^ cavalry^ and artillery^ and are especially
suited to active defence.

Fig. 10 is the smallest shelter trench that can be made, and
the least possible obstacle to advance, though from its form it
takes as long to make as that in Fig. 2, and does not give as much
cover. In Fig. 5 the cover is much better^ but the advance of
cavalry and artillery more difficult.

By deepening the trenches and heightening the parapets a great
deal more cover may be obtained, but they become less suited to
the ground over which counter-attack is intended^ and give better
cover to the enemy if he takes them. Figs. 6, 7^ and 8 furnish
examples.

In Fig. 9 the trench is the same as in Fig. 8, but the parapet is
increased to breast height and thickened, the extra earth being
got from a ditch in front.

The internal or interior slopes of parapets breast high, as in
Fig. 9, should be revetted or faced when practicable, as a man
can get closer to them and be better covered. The parapet shown
in Fig. 9 is revetted with hurdles, which are secured to a log
buried in the heart uf the parapet If revetting material is not
at handj the stiffest earth or clods should be used for this slope in
order to make it as steep as possible. If revetted, it is generally
made about -f ; if unrevetted^ from -f- to 4-* Its height should be
sufficient to protect the body of the soldier when delivering his
fire: this will depend on the depression at which he is firing
(Fig. 4, PL XIII.).

Usually a height of 4^ feet will admit of any depression not
greater than ^; for any greater depression a height of 4 feet or
less. For firing up hill, the interior slope may be 4^ or 4| feet as
the arms are more raised.

If it is required to be able to mount on to the parapet (to advance,
or to repel a bayonet attack, for instance,) steps must be sub-
stituted for the slope (Figs. 2, 3, Plate XIIL).

87. It is advisable to supplement the cover afforded by earthen
parapets by some method of protecting the heads of men firing
over them. In the case of shelter trenches a little extra beigbt
may be given to the portions of parapet between every two rifles,
and in larger works, in the same way, the parapet may be sur-
mounted with a thin earth screen with channels through it for the
rifles. Logs may be placed on the crest (Fig. 8, PI. II.), resting
on sand-bags or other means of raising them so as to leave a space
for rifles to fire through.

Sand-bag loopholes (Fig. 9, PI. II.) are the best, as only one is
destroyed if struck by a shell, and they can be moved hither and
thitber where most required.

Brushwood loopholes (Fig. 10, PI. II.), embedded in the crests
of parapets of shelter trenches, &c., or board troughs, give great
protection*

AJflMUNITION CART OR GUN LIMBER PIT.

TRENCH FOR UHBER WITH TEAM
;S2 ImaJ ft cfSof^ lirl H" T^

PIT FOR LIHBU ONLY 3 HOUHS / at } Ma/llir /tua lU

Scale ti)

LOOFHOUIS

■"* ElerrOien- .

HASTT INTBENOHMENTF. 53

88. Infantry in reserve can nearly always be oovereJ by Cover for
accidents of the ground. m^^^&J*"

The supports of the shooting line frequently stand in need of '
artificial cover ; when time is short this consists of shelter trenches Shelter trencb.
adapted to their formation (usually two-deej) line), and eiving as
much cover against rifle bullets and shrapnel as time will allow.
{See examples in PL I.). When time admits these trenches may
be made much deeper, and in exposed situations covered over (see
paragraph 112).

Charger pits can be quickly made for the horses of the mounted Shelter for the
officers of a battalion (Fig. 5, 6, and 7, PI. II.), but as it is not J^jJJSJjf '
easy to induce horses to go into them, any other cover which
nature may provide should be preferred, though it may not be
conveniently close.

The small-arms' ammunition carts, of which three will hold the Shelter for
regimental reserve, may be sheltered if necessary in pits similar •wn">n«t>on
to the limber jnts of the artillery. (Fig?. 1 and 2, PI. II.)

The horses must be taken out for this ; or a larger trench, as in
Figs. 3 and 4, PI. II., must be made.

Ccfverfor Artillery. — Gun Pits.

89. Guns can be quickly covered in a manner corresponding Cover for
to the shelter trench for infantry by means ot gun pita and epauU *«*^«'y«
ments. In the former (Fig. 2, PI. III.) the gun stands in the trench ^'*" P'*'*
excavated; this is the quickest method, but is only applicable

when the nature of the soil gives a firm wheel base, and there is
no prospect of rain rendering the bottom of the trench imprac-
ticable fi^r the gun detachment to work in.

It is better to cover guns by epaulments, allowing the carriage
wheels to recoil on the natural ground, and cutting trenches at
the front or side to cover the gun detachment.

The epaulment is raised from a ditch in front or on both Epaulments.
sides, and the gun stands on the surface of the ground. (Figs. 3
and 4, PL III.).

In either cases the main object is to shelter the gun detach-
ment, whilst allowing the gun to be worked easily.

Figs. 2, 3, and 4 can be executed by the gunners with the tools
carried on the gun limbers and wagons (viz., six picks and six
shovels).

Gun pits or epaulments may be well placed 25 to 30 yards
apart ; the usual interval between guns in action being 19 yards.

Where space is limited the pits may be closer, or it may be Connected
necessary to mass the guns in battery. Figs. 1 and 3, PI. IV., ganp>t8.
show plans and sections of a sunken battery and surface battery
respectively. It will be observed that they are in both cases
little more than connected single gun pits and epaulments. A
traverse is shown between every two guns, but this may be
omitted, and the guns placed not less than 15 feet apart, if oblique
fire be not feared, or if time press.

ELEMBNTABT FIELD FOBTIFIOATIOK.

Gun pits in

shelter

trenches.

Blinded gun-
pits.

Service of
ammunition.

Portions of shelter trenches may be enlarged into gun pits if
desired. The enlargement of the 8-feet trench (Fig. 4, PI. II.)
would only take the gun detachment three-quarters of an hour to
effect.

Guns of position require a 15 feet breadth of pit or length of
parapet per gun.

Occasionally in important and exposed situations^ it may be
necessary to blind gun pits on the same principle as field case-
mates. Descriptions of blindages for field guns and Gatlings will
be found in section 6.

Usually, the limbers and teams of a field battery in action
without artificial cover, are about 20 yards in rear of the guns ;
the wagons which supply the limbers are still further to the rear
in safe places.

If the ground will not afford shelter to the limbers, one of the
following alternatives must be adopted, viz. : —

1. The limber boxes may be taken off and i)laced in the gun

pits or in recesses made for the purpose in the manner
shown in Fig. 2, PL IV., the horses and limbers being
kept in rear under shelter.

2. The limbers may be placed in pits near the guns (Figs. 1

and 2, PI. II.), the teams being taken out.

3. Limbers and teams may be sheltered in trenches near the

guns. This, however, necessitates a much greater amount
of labour and time.

Limber-pits are best placed between the guns, retired a little
so as to leave a free passage. The third system is too laborious
to be often used, and the large trenches interfere with the move-
ments of the guns.

When guns are in battery, the ammunition boxes can be placed
as shown at MM. in PI. IV.

General prin-
ciples.

Section 4. — Obstacles.

90. Obstacles are generally used in conjunction with defensive
works, but may be constructed in the open field to stop an advance
of troops, or to increase the difficulties of a night attack.

They are particularly valuable in a close country, where a long
range cannot be secured, and the enemy, in attacking, has only a
short distance to traverse under fire. They serve also to define
the lines of attack over which an assaiLint must advance, and
thus enable preparations to be made to meet him, with some degree
of certainty. Unless much time and labour can be devoted to the
construction of obstacles in the field they are not insurmountable :
they, however, perform the part for which they are intended if
they retard the progress of troops advancing to an assault ; break
the formation of an attack ; or by keeping the enemy under the
defender's close fire, bring heavy losses on the attacking lines or
columns.

^ (HTK PITS CLOSI' I) INTO A BATTFR\ lUOIIH.
^ ^aU do)

SixamatAf^l) Fiy a.

iiliriiip Scfiu rmeUitd, inlh btrf, dad*, loc.
Hit IhmfK* ran btr An-lutxrtl £ h-aglilmrJ in a

OBSTAOLDS. 55

N^atural features of ground maj sometimes be converted into
serious obstacles with yery little labour; steep places may be
made precipitous^ deep cuts or holes may be dug m shallow water,
wet ditches or inundations may be formed, &c.

The general conditions under which obstacles should be con- Conditions
Btructed are as foUows :- TlHl^litSSL'**

(1.) They should be under the close musketry fire of the
defenders.

This will be the case if they are within 300 yards of the de-
fending line. It is advisable, however, not to pkce the obstacles
too close to the defenders when the latter are only protected by
shelter trenches, or other cover presenting little or no impediment
to an infantry advance, as the moral e&ct of the presence of the
attacking force within a few paces might be disadvantageous. It
will be better in this case not to place the obstacles nearer to the
line of defence than 50 yards. When, however, the defenders
are protected by a parapet and ditch of good profile, these of
themselves give them confidence, and the above argument does
not hold good.

(2.) Obstacles should not afford cover to the enemy. Thia is a
self-evident condition, placed as they are within the
most efiPective range of the defending line.

(3.) They should, if possible, be protected from the enemy's
artillery fire, so as to be intact when his infantry comes
upon them, and they should be diflicult to remove or to
surmount.

(4.) They should be arranged so as not to interfere with a
possible advance or counter-stroke against the enemy.
When such is contemplated, gaps should be left suffi-
ciently large for the purpose in view (150 yards is
sufficient for the front of a half battalion deployed for
attack, and will also allow space for the passage of
cavalry and artillery).

The obstacles usually employed are described in the following
paragraphs.

Abatisy Entanglements^ Sfc,

91. One of the best obstacles that can be made is an ^'abatis*' Abatis.
formed of stout limbs of trees 12 or 16 feet long, laid as close
together as possible, with the branches towards the enemy. The
abatis should be at least 5 feet high, with the butts buried in the
ground, secured by stout stakes, or by logs of timber laid across
several butts. The large branches should be pointed, and the
small branches and leaves removed. They may be placed in the
ditch of a work in an upright position (Fig. 1, PI. V.) or, as is
more usual, in advance of the ditch. In the latter position an
advanced glacis may be thrown up in front of the abatis to protect
it from artillery fire (Fig. 2, PI. V.), but even without this it is
not easily destroyed.

ELRMRNTART FIELP FORTIFICATION.

The labour of drag^n$c the trees required from a distance being
very heavy, the construction of an abatis should not be attempted
unless the trees grow near at hand. Hard and tough woods are
the best, pine being the worst, as it is easily broken and bnms
readily when fresh cut, which is not the case with hard woods.

Time. Twenty men can make an abatis of two rows, 30 yards loaf(, in

six hours, when the trees are small and close at hand. One half
felt, point branches, and drag the trees into position ; the other half

Tools. fix the trees and picket down the butts. They require 6 felling axes,

2 hand axes, 6 bill hooks, 2 hand saws, 2 msdlets, and dr^ ropes.

Entanglement. 92* An entanglement U a kind of abatis, formed by cutting the

trees, brushwood, &c., half through, about 3 feet above the ground,
bringing the upper parts down to the ground, and interlacing and
.securing them by pickets. Large trees thus treated form almoet
insurmountable obstacles. The ends of thick branches should
be pointed, and all weak places strengthened by ordinary abatis.
Vines woven together, with their tops picketted to the ground,
form good entanglements.

The tools and time required for this nature of obstacle must
vary according to the material of which the entanglement is
formed ; axes, saws, billhooks, and maMets, with some ropes, are
generally used.

Wire en-
tanglement.

Time.
Tools and
materials.

Jones' gabion
trip for
cavalry, &c.

Chevaux de
frise.

93. For wire entanglement^ stout stakes are driven into the

ground, from 4 to 7 feet apart, in rows arrauged chequerwise, and

their heads connected by strong wires crossing diagonally, twisted

round the heads of the stakes, about 1 foot or 18 inches above the

ground. (Fig. 3, PI. V.). No. 14 B. W. gauge, a mile of which

weighs about 90 lbs., is a convenient size of ^Yire to adopt. This

obstacle is rapidly prepared, very portable, little injured by

artillery fire, and impassable by cavalry. The entanglement

should be at least 10 yards in depth. It is most effective when

constructed amongst brushwood, small bushes, &c.« which

conceal it.

Five men should make a wire entanglement, 50 yards in length
and 10 yards in depth, in 10 hours. For its construction, three
bill-hooks, one mallet, two pincers, 150 pickets, and 900 jvx^
wire are required.

94. The bands of Jones' iron gabions {see Siege Works)
may be formed into a network or entanglement as an obstacle
against cavalry, and even ag<ninst infantry in night attacks. The
bands are buttoned and placed in line 3 or 4 feet apart ; each
band is connected with the next by stout wire or rope passed
through the bridging holes. Bands thus connected should be W
in parallel rows chequerwise, 3 or 4 feet apart, the rows being ^^
connected by wire or rope, and secured at intervals to pickets
driven into the ground. (Fig. 4, PI. V.)

95. A pattern of chevaux-de-frise forms an article of store.
The barrel consists of a hollow iron tube, 6 feet long, with holes
through it at intervals tor the spears. The latter, 12 in number,
are 6 feet long and pack inside the barrel. Each length of barrel
with its spears weighs 86 lbs.

OBSTACLE S .

CHEVAUX-DE-FBISE (IMPROVISED)

lY PITS

DEEP Ml LITARY PITS

OB3TAGLBS. 57

Chevaux-de-frise can be improvised of iron pipes^ or stout
beams about 6 inches in diameter or square^ having pointed poles
or spears about 6 feet long, fixed to the beam by nails^ spunyam,
&c., or by being passed through holes bored through the pipe.
The poles are made to cross each other at right angles and should
not be more than 6 inches apart ; these spears should be strong
enough to prevent a man breaking them. Improvised chevaux-
de-frise may be made in lengths of from 6 to 10 feet, and should
be secured together by stout iron wire or chain. (Fig, 1, PL VL)

96. Palisades are a stout description of paling, vertical or Fiiaitftdei.
nearly so, made of large branches of trees, logs of timber, or young

trees split or sawn into two or more pieces, according to their size,
pointed at the top, and secured to two horizontal bars or ribands.
The posts, about 10 feet long, are often made triangular in section
(each side being 7 or 8 inches) and are placed upright about
4 inches apart, their lower ends being spiked to a riband and
planted in a narrow trench from 3 to 4 feet deep. The trench is
then ^lled in with earth, well rammed, and an upper riband is
nailed on the inside of the posts about 1 foot below their tops.
An expeditious mode of constructing a palisade is to prepare and
plant it in panels of four or five posts each. (Fig. 2, PI. Vl.)

Palisades may be used for the defence of ditches, and for closing
the gorges of field works. When planted near the foot of the
counterscarp, the ditch in rear of them shculd be deepened, and
made V shaped. This section of ditch prevents an enemy froni
forming up in it, and so entering the works in mass.

97. Praises are palisades placed horizontally, or nearly so, I^niaes.
in the slope of the escarp or counterscarp. If in the former, they
should be inclined slightly downwards, and should have their
points not less than 7 feet above the bottom of the ditch, that they

may not assist an enemy climbing up ; if in the latter they may
be inclined upwards to increase the drop into the ditch (Fig. 3,
PJ. yi.). The posts should be about 1 1 feet long, so that 5 feet
may project beyond the scarp ; the ridges should be uppermost,
to increase the difficulty of standing on them ; they should be
nailed to two ribands both buried, the one nearest the scarp below,
and the other above the po^ts.

Fraises should be of such strength as to prevent an enemy
breaking them by his weight, and may be advantageously placed
2 or 3 feet below the crest of the glacis, so as to be protected from
the eneaiy*s fire. To increase the difficulty of leaping into the
ditch, pointed stakes or vertical abatis may be placed under the
ends of the fraises.

98. The small branches cut from abatis may be rendered Pointed stakes.
usetiil by being made into stakes. After being driven into the

ground until 1 or 2 feet only project, the upper ends should be
sharply pointed. Tbey would seriously hinder the advance of the
enemy if placed on the ground in front of the counterscarp, in the
bottom of ditches, or on the berm.

42642. E

ELEMENTABT FIELD FOBTIFICATION.

Crow's feet.

Harrows, &c.

Military pits.

Construction of
deep pits.

Time.

Tools and
materials.

Construction of
shallow pits.

l^e.

Tools and
materials.

99. Crowds feet are formed of four stout spikes 2^ or 3 inches
long, welded together at their heads, in such a manner that in
whatever position they may be, there will always be one point
uppern\ost (Fig. 5, PL VI.). They are very useful as impediments
against cavalry, and may also be placed in fords, &c.

On the glacis, harrows may be buried with the spikes ex-
posed, or broken wheels and large rough stones may be strewed
about to break the order of the assailants. Broken bottles and
glass may be scattered about, put at the bottom of ditches, or on
die tops of walls.

100* Military pits (French, trous^de-loup) are excavations in
the shape of an inverted cone or square pyramid, with a pointed
stake at the bottom.

They are of two descriptions, viz., deep and shalloto ;. the former
are more advantageously used when they can be flooded, as other-
wise, with every care in their construction, they may form con-
venient rifle pits for an enemy's skirmishers ; the latter are made
BO shallow as to avoid this.

The deep pit is made 6 feet in diameter at the top, and 1 foot
at the bottom, the depth varying from 6 to 8 feet, with a stout
stake planted in it with its top flush with the ground. Those
shown in- Fig. 4, PL VI., are of a convenient size, and are usually
placed in three rows, the pits being 10 feet from centre to centre,
the excavated earth being heaped up on the space between them.

One man should dig a pit in 5 hours, llie tools required are
1 pick, 1 shovel, 1 stake ; also a mallet and a biUhook for eveiy
20 men, and a 6-foot rod for the non-commissioned officers.

The shallow pits are shaped like inverted pyramids 3 feet
square, and not more than 2 ft. 6 in. deep. They are placed in
rows touching one another, in a zig-zag arrangement, as shown in
Fig. 1, PL VII. Five rows are usually made, and the earth
excavated is thrown to the front to form a glacis. The rearmost
row is first formed, so that the earth excavated from any one pit
may not have to be thrown over those previously excavated. A
pointed stake should be placed in each hole with its top flush with
the ground line. A combination of shallow pits with a wire
entanglement over them is a most formidable obstacle.

One man should dig 10 pits in 8 hours. The tools required are
1 pick, 1 shovel, 10 stakes; also a mallet and a billhook for eveiy
' 20 men, and a 6-foot rod for the non-commissioned officer.

Barricades.

lOL Barricades are used for the defence of streets, roads,
bridges, &;c., and may be made of almost any materials that
happen to be on the spot. Furniture, overturned carts, casks
filled with earth, timber, heaps of stones, rubbish, iron railings,
bales of goods, &c., can all be made available (Figs. 2 and 3,
PI. VII.); but earth should be used where the barricade is
exposed to artillery fire. When trees grow alongside a road it
may readily be barricaded by felling them across it.

OBSTACKKS

SHALLOW MILITARY PITS -
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a J._i^__^:^:wil-^"^

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OliSTATLES.

FOUGASSE.

OBSTACLES. 69

Banquettes should be formed, and the barricades should be
flanked both in front and rear from loopholes in the adjacent
houses or walls (when such exist), communications being made
from house to house on each side of the street to allow of fire
being kept up on an advancing column, and to enable the flanking
parties to retreat. The loopholes should be arranged, as much as
possible, so as not to fire into each other ; and the defenders, on
being posted, should be cautioned as to the direction of their fir^.

The doors and windows on the ground floor looking into the
street on each side of a barricade should be blocked up, to prevent
the enemy forcing an entrance, and driving out the flanking
parties.

Passages, to allow of the advance or retreat of outposts, are
generally required through barricades. This can be arranged by
making the barricade in two or more parts, overlapping each
other, as shown in Fig. 3, PI. YII., or by placing the barricade at
a sharp bend in the road, or where a house standing back from
the general liue of building affords a good fire on the passage
round it. (Fig. 4, PI, VII.) One or two lengths of chevaux-
de-frise should, if possible, be at hand to close up the openings
round barricades.

Faugasses.

102. Xfougasse is a kind of mine charged with powder. Over Fongasse.
the powder, stones, bricks, and sometimes live shells, are piled.
When fired, the superincumbent material is projected over a
considerable surface of the ground in front.

Fougasses, when used in the defence of field works, should
be placed at least 12 feet in front of the counterscarp to prevent
injury to the latter.

For a stone fougasse, an excavation is made in the form of the
frustrum of a cone or pyramid, a box of powder is placed in a
recess at the bottom, and on the box a wooden platform or shield
three or four inches thick ; over the shield the stones, &c. are piled.
The axis of the cone should be inclined at about 40° with the
horizon, varying a little more or less as the ground in front is
ascending or descending ; the sides should form an angle of about
12° with the axis.

Fougasses may be fired by electricity, or by hose and fuze
passed through a hole in the box, a grove being cut in the back
of the excavation to receive the wires or fuze and to protect them
from injury during the operation of loading, which should be
performed with great care.

The fougasse shown in Fig. 1, PI. VIII., charged with 80 lbs.
of powder, would throw five tons of bricks and stones over a
surface about 160 yards long by 60 yards on either side of the
lin of the axis.

The L.L.R.* must be so arranged by placing the excavated earth
on the back edge of the fougasse, at a, that the powder will act
in the direction of the axis, and not vertically.

* L.L.B. means line of least resistance.

E 2

ELEMENTABY FIELD FOBTIFICATIOy.

Shell foQgiiM. A shell fouffosse is a wooden box buried in the ground, the

lower part filled with powder, and the upper part with fuzed
Bhells.

Inondations.

Dams.

Was'e weir.

Inundations,

103. When a position is occupied near a stream, the water
may sometimes be retained by dams, so as to accumulate in iront
of the line, and thus form an inundation. When the inundation
is to be shallow, before damming up the stream, ditches should be
cut chequerwise through the ground to be inundated, of sufficient
depth to prevent wading, and crows* feet, harrows, &c., may be
scattered about and deep military pits dug. The most favourable
positions for forming inundations are those where the bed of the
stream has only a slight fall, and the sides of the valley are regular
and rise rather rapidly ; where these features do not eiiist, the work
is generally too extensive to be undertaken.

In making an inundation, the embankment on each 8ide of the
stream should be completed first. The soil of which the dam is
composed should be impervious to water, or if it be not, a wall of
puddle clay* should be constructed inside it. If there are to be
two or more inundations, the materials for the dams should be
taken from the lower side, so as to increase the deptli of the next
inundation. Great care should be taken to ram the earth forniing
the dam. The chief difficulty is always encountered when con-
structing the part over the bed of the stream, which should be
done as rapidly as possible, as when once the stream is dammed up,
the dam must keep pace with the rise of the water. Materials
should be collected below the dam, and on each side of the stream,
and as large a working party employed as can work together, A
bank of earth is first made across the opening, between the two
finished portions of the dam, to enable the foundations of the
remainder to be put in. The thickness of the dam at top may be
made equal to the depth of water retained ; the slope of the up-
stream side is usually made ^, and of the lower side \. When
exposed to artillery, the top should be made thick enough to resist
the fire.

Unless the surface of an earthen dam be protected, it will soon
be washed away by any water flowing over it ; a waste weir must
therefore be made large enough to carry off all the water of the
stream. A channel for a waste weir should be cut through the
solid ground, clear of the dam, if possible, but if not, it must be
formed in the dam itself. It can be made of fascines if planks
and timber cannot be procured. The bank near a weir roust be
constructed with extra care, and should be well revetted ; this revet-
ment should extend beyond the foot of the dam on the lower side,
so as to protect it from the rush of water over the weir. A double
layer of fascines, securely picketed, forms a good revetment. The
surface of the weir should be two or three feet below the top of
the dam, according to the liability to floods. Dams and waste

* Clay is puddled by being well kneaded with a smaU quantity of water.

DKI'KNSIBLE IIEUGKS.

ADAPTATION OF ACCIDENTS OF Tllfi SURFACE. 61

'weirs may be constructed of timbers roughly framed together, and
covered with a layer of clay. (Figs. 2, 3, PL VIIL) Sluice
gates are occa^iionally required to dram the inundations.

An inundation may sometimes be formed by damming up the
arches of a bridge.

The ditches of field works, when of good pmfile, form of them- Ditdiet of
selves a considerable obstacle, which is greatly increased if they ^^^ woriw.
can be flooded. This may frequently be done, especinlly in the
case of bridge head^, by damming up the natural course of the
stream, and diverting it through the ditches.

Section 5. — Adaptation of Accidents of the Subface.

Defensible Hedges*

104. Hedges may, according to the nature of their gro?rth, and
the suitability of their position, be used either as obstacles, screens,
or revetments, fulfilling at once any one or more of these purposes ;
a hedge by itself, though it mny break the force of a rifle bullet,
cannot be considered as afibrding any cover.

. As an obstacle, a hedge had better be left standing, subject. As an obsttcle.
however, to its not impeding the defenders* view of the enemy.
{See sect. 2, on clearing ground.) Otherwise, and especially if
large and strong, it may be treated as brushwood entanglement
(sect 4J.

Ditch and bank hedges (Fig. 1, PI. IX.) can often be used as Ab scieen,
they stand, or with very slight deepening of the ditch, the hedge revetment, &c.
acting as a Fcreen, and the men firing from between the stems ;
thus the hedge is at once a shelter trench and an obstacle. In
Fig. 2, where there is no bank or dit<;h, the shelter trench has to
be artificially supplied.

In Fig. 3 a hedge is used as an exterior revetment to a parapet
6|: feet high, the eailh for which is excavated from a shallow
rench in rear, altogether providing superior cover from fire and
view, but requiring much more time for preparation. The height
of 64 ft. prevents the enemy from firing over the top in the event
of the defenders' retreat ; this may abo be attained by making a
small ditch in front, as in Fig. 4. Here the hedge is better than
an outer earthen slope, as it is an efiective obstacle, and diminishes
the amount of excavation for the parapet. Hedges must be
closely grown to be (flicient in retaining earth, though thin places
may to some extent be strengthened by weaving in loose branches.

For firing through thick hedges, loopholes must be systemati-
cally cut in them ut 3 or 4 feet intervals.

Deep cut country lanes with hedges on either side can be
prepared as shown in Fig. 5.

In Fig. 6 a hedge is used as a screen and revetment to a gun-
epaulment.

WalU.

105. In putting walls into a state of defence, loopholing or notch- Walls,
ing is the usual work to be done, chiefly the latter on account of the

ELEMENTARY FIELD PORTITIOATION.

Loopholes.

time and tools required for the former; the height of the^rall
and the elope of the ground in front of it will regulate the position
and direction of the loopholes. The general principles are to make
the loopholes at such a height above the ground in front that the
enemy will not be able to fire through them should he get up
to the wall ; and to provide complete cover for the defenders.

Looi)holes or notches are mnde in walls with crowbars, mason's
(18^') chisels, and hammers, or with pickaxes; the former should
appear from the outside as narrow vertical or horizontal slits
(generally 3 inches wide) ; when vertical, the length depends upon
the amount of elevation and depression required, and is usually
about 12 inches: when horizontal, lateral range more than
elevation is required ; a length of 2 ft. 6 ins. will accommodate two
men. Internally, loopholes are made with a splay to allow of
lateral range and elevation and depression as may be required.

A loophole generally takes 15 minutes for one man to make : a
notch or cut about 5 minutes. If cuts are made the top of the gap
should be filled up with blocks of wood, sand bags, or large stones
to cover the head. (Figs. 7, 8, 10, PI. X.) If it is intended to
fire over the top of a wall, a log resting at intervals on sand bags
may be used, or sandbags only (Figs. 3, 4, 9, PI. X.).

While walls will protect the defenders from shrapnel fire and
splinters of shells, they will not resist the common shell from field
guns unless they are of unusual thickness, 3 feet and upwards.

When walls are required to give complete protection against
artillery fire it is necessary to strengthen them by a thickness of
6 feet to 8 feet of earth, or by an earth screen of that thickness
made in front of the wall. (Figs. 1, 2, 3, PI. XI.)

Where these screens are necessary it is advisable to flank both
the excavations from which the earth is procured.

Several methods of preparing walls of different height for
defence are given in PI. X.

If the wall is only 4 feet high the defenders would fire over the
top, and a ditch should be cut in front, the earth from which
should be spread about ; a trench in rear will improve the cover
(Figs. 1, 2, 3, 4, PI. X.).

When the bottom of the loophole or notch is more than 4 ft.
above the ground inside, a banquette must be formed in rear, of
earth, or any planks, barrels, or trestles that may be at hand
(Fig. 8, PI. X.).

Two tiers of loopholes are very useful, especially in flanking
barricades, long lines of walls, &c. : — they can be made in various
ways according to the means available (Figs. 9, 10, PI. X.).

EmbankmentB.

Embankments^ Cuttings^ Boads, 8fc,

106. Embankments parallel to the front afford cover for sup-
ports and reserves, or can be adapted for the shooting line in either
of the ways shown in Figs. 2, 3, PL XII. The method at A
answers best for low embankments, as it gives better cover; if tlie
embankment is very high or broad so that fire from the position

Fu, I UKKENSIBLK WALLS.

■^!tiiiiii"ii'iintnt!!ii

SCKEENED WALL.

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F.F. Plate XU.

CUTTINGS A KWBAXKMKXTS.

CUT ROAD

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EMBANKMENTS.

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tlrtanys Sight-

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FIELD WOBK8. 63

A would leave its foot undefended, it would be better to
occupy the forward edge, as at B.

Cuttings parallel to the front afford in the same way cover for Cnttiiigt.
supports and reserves posted in them. If occupied by the shoot-
ing line, one of the two methods shown in Fig. 4, PI. XII., may
be employed. The method at A is the best for active defence,
but retreat is difficult, and must be provided for by steps or paths
cut up the rear slope of the cutting. The method at B has the
advantage of the cutting forming a large ditch in front, and of
retreat being easy. Both methods A and B might be employed
in the same cutting, in order that retreat from A might be
covered by the fire from B.

A road cut on the side of a hill is easily convertible into a strong
shooting line, as shown in Fig. 1, PI. XII.

Soad drains and other smidl ditches can often be used as 'Bead dnint. .
shooting trenches, or to cover supports.

Wooden palings can be used as screens or revetftients (Figs. 5, J^iinga and
6, PI. XII.). Post and rail fences may be boarded and made to *"^***
act in the same way.

High standing com may be useful as a screen along the shooting Standing com.
line, in which case a narrow belt of it can be left standing.

The reverse slopes of hillocks and undulations should always be Irregnlaritict
made use of to give or to improve cover or concealment Figs, 7, 9, ^ g^vad.
PL XII., are equally applicable to infantry ; Fig. 8 shows how
the cover is improved by notching the crest Fig. 9 shows how
a hollow may be used to screen guns.

Beverse slopes nearly always screen, but do not as invariably
afford cover from fire ; for if the depression of the slope coincides
with the fall of the enemy's projectiles, and the latter move
consequently parallel to the surface of the ground, the cover from
searching curved fire is no better than if the defenders were on
the leveL Nevertheless, concealment firom view must not be
under-rated. The chances of being hit are so much less, and the
enemy does not know whether his fire is effective or not.

Section 6. — Field Woeks.

107- It has been seen that of all the forms of cover, earthworks Q^nend
are best able to resist artillery fire. But the earthen parn pets before principles,
described have been of a slight character, suited either to cases in
which there is not sufiicient time for anything better, or to the
advance of troops over them to the counter-attack.

When superior cover as well as obstacle to Assault is required,
earthworks must have larger dimensions, that is, higher and
thicker parapets and deeper ditches, and be capable of sheltering
their garrisons from artillery fire.

JProJile,

108. The parapets should be at least 6 feet high (more, if pos-
sible), above the ground, and the bulk of the earth for the parapet

ELEMENTARY FIELD FOUTIFIGATIOK.

Plane of site.
Command.

ReUef.

Terrepleio.

Banquette.

^teps of ban-
quette.

Exterior slope.

Berm.

should be got from a ditch outdide, the form of which may be aucli
as to offer an obstacle to assault. A trench in rear as well (in the
case of works subject to artillery fire) greatly increaaes the pro-
tection from curved fire, enabling the defenders to move si^elj
along the rear (Fig. 1, PI. XIII.).

The slopes of these larger parapets should be regularly formed
to enable the defenders to use their weapons with efiTect, and to
increase the durability of the work. IF time does not press, tke
earth should be rammed as the work proceeds.

Fig. 1, PL XIII., explains the names of the different slopes of
the parapet and ditch.

The intersection of the superior and interior slopes .is called the
interior crest or crest ; that of the superior and exterior slopes
the exterior crest,

A plane generally tangent to the ground on which a work is
constructed is called the plane of site, and the vertical height of
the interior crest above it at any point is called the command
of the parapet at that point.

The term command is also used to express the height of the
crest of one work above that of another, or above any particular
point within range.

The relief of a work is the height of its crest above the level
of the foot of the escarp.

The terreplein is the surface of the ground within a work.*

For all parapets of greater command than 4^ feet a small
terrace or banquette is required to enable the defenders to use
their rifle?.

The width of the tread of banquette for a single rank should
be 3 feet (though 2 feet may serve at a pinch), for a double rank,
4 feet; it should have a slope of 2 or 3 inches to the rear for
drainage. The slope of banquette is usually not steeper than \i
unless the banquette is low enough for a man to step on to it a^
once, when the slope may be \ (Fig. 9, PI. XIII.). If revetting
material is at hand, room cap be saved and the cover improved
by substituting steps for the slopes of banquettes; they may
have a rise of 9 inches to 18 inches, and a tread of 12 inches to
18 inches. A 9-inch rise is convenient for revetting with fascines
(Fig. 2, PL XIII.). Boards kept upright by means of wooden
pickets or short lengths of iron pipe, &c. make good steps (Fig. 4,
PI. XIII.).

The exterior slope, being exposed to fire has generally a slope
of \ (the assumed natural inclination of ordinary earth ; with very
loose earth or sand, the gentler slope of § would be better.

The berm is left for stability only, and, as it gives the
enemy a footing in scaling the parapet, should be as narrow as
possible. It may be from 1 to 6 feet wide according to the
stifihess of the soil and weight of the parapet, but if wider than
3 feet should if possible be strewn with obstacles. In works not

♦ Terreplein in terre plain misspelt, bat the error is now too long establifthed for
correction.

: OLACIS

DITCH

F.F.i'iau xm.
ll !

TBI NTH

"' I r;!"T

AREA OF DJTCH

AREA OF SECTION
OF PARAPET.

DITCH Oil ftUOPlNC OROUNP

Sealm

ARIA OF OITCH.

msac - ah t de.

wmmm,

Fiq. a

PROFILES offovutt ARTILLERY.

Very Uxt^r earth er sand

f /hUripr Slept unrtveM^elJ

W//1

Wfm

forRgg. G, 7.Ad.(27o)

J Pace per man
pm-RetiefoCShrs.

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IOto 15 HOUR PARAPET.

Turf LoiophaUs

Working Farty

2peu»a t^ Relief.

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FIELD WOBK8. 65

required to last long, and In those of alight profile^ it is better to
omit the berm, making one slope of the exterior dope and
€9carp.

The ditch, to be an efficient obstacle, should not be less than Ditch.
6 feet deep and 1 2 feet wide at the top. A narrow bottom (about
2 feet broad) is best as it does not give the enemy so much space
to assemble in, previous to scaling the parapet (Figs. 1, 6, 7,
PI. XIII.). Owing to labour of construction 12 feet may be
considered the maximum depth for the ditches of field-works.
Usu^Uy a depth of 9 or 10 feet would not be exceeded. Deep
ditches are as a rule to be preferred as obstacles to broad one&

When the ditch is small, the greatest value as an obstacle is
obtained by making it V-shaped with escarp and counterscarp
sloping I (Figs. 9, 10, PL XIII.).

When the ground slopes, the bottom of the ditch is usually made
parallel to its surface in order that the depth shall be uniform.
(Fig. 5, PJ. XIII.).

The escarp and counterscarp should be as steep as the soil Ecearp and
will allow ; the former less so than the latter, however, on account ^'™*«"C"P'
of the weight of the parapet near it. The escarp may slope from
\ to -f-, the former being advisable for works that are to last some
time ; the counterscarp from \ to -f-

When opportunities exist for letting water into ditches their VfTet ditches,
value as obstacles is increased; the gentlest slopes here given
should in this case be used for escarp and counterscarp. Near the
point of entrance of the stream, it will often be necessary to revet
the escarp and counterscarp and to floor the bottom.

The thickness of the parapet is measured horizontally be- lliickness of
tween the crest and exterior crest (Fig. 1, PI. XIII.). This P«P«*-
should not be less than 3 feet, even against musketry ; 6 to 9 feet
will usually be sufficient against light field guns (9 pr.), 9 to
12 feet against heavy field guns (16 pr.), 12 to 18 feet against
guns of position. The nature of the soil must also be taken into
account.

The superior slope ought to be so regulated that the fire Superior slope,
directed along its surface may pass not more than 3 feet above
the outer edge of the ditch. With an ordinary command, on level
ground, a slope not exceeding \ will fulfil this condition; if the
ground falls to the front a greater slope than this would be
necessary, but it should never exceed \ in any case (this with an
interior slope of \ makes the angle at the crest 90°). To avoid
weakening the top of the parapet it is ];>etter to make it gentler
than ^, (f , or J) if possible ; if the outer edge of the ditch is then
not properly defended, a glacis becomes necessary (Fig. 1, Glacis.
PI. Xill.), to ensure the assailant being brought under fire. The
crest of the glacis should not be less than 5^ feet below the
level of the crest of the parapet, to prevent the enemy from seeing
into the work. The interior slope of the glacis may be -f, and
the slope of the glacis should be parallel to the superior slope of
the parapet in order that the defenders' fire may sweep its surface^
passing not more than 2^ feet above it.

ELSMENTABT FIELD FOBTIFIOATIOK.

Comnuuid.

Command
affected by the
ground.

Bear trench.

Effects of
artillery fire
on earthen
parapets.

109. The greater the command of a parapet, evidently the
better cover it affords, but the volume increases so rapidly with
the height, that the time and means at disposal very soon fix the
limit; 6 feet is the minimum command that will screen the
interior during the close attack on level ground ; but to allow of
the parapet being reduced by artillery fire it is better to increaBe
it to 7^ or 8 feet, which is therefore the usual command for field-
works when time is available. A command of 10 feet, or at the
very outside 12 feet, should never be exceeded, as the time and
labour of execution become too great for this class of fortification.

The command of parapets is a good deal affected by irregularitieB
of OTOund. Sometimes a high parapet is necessary to enable the
defenders to see ground which would otherwise not be under their
fire (Fig. 5, PI. XIV.), or to screen the interior of a work which
is unavoidably commanded by the enemy. When the terreplein
of the interior produced passes above the enemy's poedtion; the
cover is naturally better and parapets need not be so high (Fig. 6,
PL XI V.) ; but if the contrary is the case (even though the
defenders be in a commanding position), the interior is as it were
tilted up to meet the enemy's fire, and the parapets must be higher
(Fig. 7, PL XIV.).

110. The rear trench must not be less than 5 feet wide at the
bottom and deep enough to give the men standing at the rear of
it cover against curved fire (Figs. 6 and 7, PL XIII.),

The angle of descent of the enemy's shot evidently varies with
his position (whether commanding or not) and the range. The
angle of fall of the 9-pr. M.L.R. shell at 8,000 yards is about {,
for good protection this depression should be calculated on,

more especially as with shrapnel the dispersion of the bullets (6^
or 7^) increases the depression. The greater the command of the
parapet, the less deep need the rear trench be.

Complete protection is obtained by blindages as described later
(Fig. 8, PL XIII.).

Figs. 9 and 1 0, PL XIII., give examples of profiles of parapets
with a command of 6 feet, suitable for resisting musketry fire.
Figs. 6, 7, 8, PL XIII., are intended to resist artillery fire.

Fig. 7 illustrates the great advantage, as regards cover, of
revetting the interior slopes of parapet, banquette, and trench ;
the cover at the rear of the trench being 7 feet, against an enemy's
fire descending at J ; whereas, in Fig. 6, where the slopes are all
unrevetted, the same depth of trench does not give nearly as good
protection. These profiles are suitable for enclosed field-works
at important points where power of holding out for some time is
desired.

111. The damaging effects of artillery fire on an earthen
parapet are as follows : —

The crest is shot away, and the superior slope receives indents
and irregularities which interfere with the fire from the parapet.
The exterior slope and upper portion of the escarp are shaken and
covered with holes, which serve as foot-holes to the assailant, the
earth falling into the ditch and reducing its depth. Sharp angles

F. F.PUtcHf

OpptopageGC

Su^ei^cild. 22 Eftafiord. S^ Co-v^ni G«ird«a

FIELD WOBKS. 67

and slopes finally disappear^ the parapet becomes a shapeless mass,
and much earth collects at the foot of the escarp and banquette.
The glacis is covered with furrows 3 or 4 feet long and about 1 foot
deep. The destruction of an earthwork does not, however^ prac-
tically go beyond certain limits, and the thickness at top would
probably not be diminished more than a couple of feet, nor the
creet reduced in general height more than a foot or 18 inches.

112. The dimensions of all the embanked earth being settled, Determining
the contents of the excavations must be balanced to correspond. If |^^ ]Xf^^
the soil is very stiff, though well rammed, or if there is not time fieid''\\orkB.
to ram at all, the excavated earth will not occupy so small a space
as before excavation, and this should be borne in mind, although
as a rule the difference need not be taken into account in the
calculation, as the surplus will always come in for other purposes.

The following example explains the calculation for the width of
the ditch: —

In Fig. 1, PI. XIII., the section of parapet is either calculated
piecemeal (dropping verticals from all the angles), or it is reduced
to a triangle by geometrical construction, and its base {be) is
found to measure 34 feet, say. The command being 7^ feet, the

Area of the triangle (abc) = — - —

sq. ft.
" =^|j^ = 12n8q.ft. .

Areaofgkcis=i (13ixli) = ^?^2

= V = ioj

Total embanked earth = 127^+10^ = 1 38, say.
Bear trench, to be deducted = 21
.'. area of section of ditch=138— 21 = 117=rectangle {eg)^
or €fxfg=:\\1, and if ^/=10, r.fg^X^^ = 11^.

Note. — (ef) and {gs) are verticals drawn through the centre
points of the escarp and counterscarp.

Trace of Field Works,

118. Wherever increased power of resistance is sought for by General prin-
means of defensive works, their general plan, called the Z'race,must c'P^es.
be entirely subservient to the tactical requirements of the case.
Whilst providing cover for all troops engaged, the works must not
hinder counter-attack, where such is required ; the more active
the defence, the less desirable is the general use of the stronger
profiles, which are obstacles to the advance of friends as well as
to the entrance of foes. A compromise must, therefore, be made
between the two conflicting conditions of strong profiles with
obstacles^ and freedom of forward movement^ giving more or less
value to either condition as may be most expedient under the
circumstances.

68 ELEHENTABT FIELD FOBTIFICATIOK.

Frontal and When troops adyancing to the attack of a position are subject

flanking fire. ^^ g^^ proceeding from any one direction, they are naturally led

to form a front towarda the point from whence it proceeds^ in
order themeelves to oppose it, and by their formation to diminish
materially their chances of loss ; added to which, the sliorhtest
irregularities of the surface of the ground will be of serxice in
affording temporary concealment, and to some extent cover.

If, however, they are exposed to fire from more than one direc-
tion at the same time they will suffer loss of morale as well as
actual loss, in proportion as the convergence of that fire deprives
them of the advantages of open formation or cover from the
ground. Hence the great value of flanking fire, but et^pecinlly of
combined frontal and flanking fire.

At the long ranges at which engagements with modern weapons
usually open, it is not generally possible to employ flanking fire
more properly so called, but at best a moderately converging (or
cross) fire, and hat of guns only. Moreover, at the same distance
of the opposing forces, the more convergent the fire the greater
the range.

Rifled arms have, therefore, in the earlier stages of an eng^e-
ment, given more importance to a strongly developed frontal fire.

As the distance between the contending forces lessens the power
of convergence of fire becomes greater, and flanking fire especially
when the enemy is stopped by an obstacle is here of great value.
To draw, then, a comparison between the former and present
arrangement of intrenchments for producing fire, so much of the
effective work of the fire combat is done at ranges impossible to
the old musket, that the chances of bringing essentially flanking
fire to bear, as heretofore, are materially lessened, although when
it can be used its efficiency, weapon for weapon, is largely increased,
and the production of frontal fire has relatively a greater import-
ance. To insure, therefore, an efficient defence, there must be in
general a good frontal fire during the earlier stages, not forgetting
cross fire where possible ; and during the close fight, an effective
flanking fire, in addition, from positions secure from assault.

The principle which best meets all requirements and admits of
expansion or contraction under ever-varying conditions, is to
fortify (as strongly as time will allow) at intervals along the line
to l)e defended, farms, villages, woods, &c. ; or in default of these,
to construct earthworks of strong profile, within reach of one
another's fire, and having a cei*tain proportion of the troops told
off to hold them with more or less obstinacy, according to their
situation. The remainder of the troops are free to take up
positions between or in rear of them, Furnishing as much fire as
may be required over the whole front, and keeping reserves dose
at hand, ready to reinforce or counter-attack, as the case may be.
The whole of these troops, whether firing, or in support or re-
serve, must be covered as much as possible from the enemy's fire>
or at least screened from his view, using and adapting for them-
selves existing circumstances of the ground, and throwing up

FIELD WORKS. 69

shelter trenche?, &c. when in the open. Thus the fortified pointfl

(called supporting points^ or pivots of the line) detain the Supportiii^

enemy, and break his line, enabling the dcFenders' reserves either ^Jj ^

to deliver a rapid counter-attack under favourable circumstances^

or to meet on more than an equality such troops as may manage

to press through the intervals. Obstacles may be freely used

around the supporting points, but their use in the intervals

between them, as well as the character of the cover provided for

the manoeuvring troops (sometimes called the outer troops)

must depend on the extent to which personal collision with the

enemy is courted. (Fig. 1, PI. XV.) • •

In all the diflPerent cases in which field fortifications are intended
to cover and assist the action of large bodies of troops, this prin-
ciple of fortifying pivots is adopted with slight modifications
for each case. These pivots are the portions which, with eartti-
works especially, require most time to elaborate, and particularly
call for the services of the field en«;ineer.

In certain restricted situations, where the defence has a purely
passive object, and when there is suificient time, lines of earthen
parapet of the stronger profile may, in conjunction with obstacles,
close the spaces between the supporting points, and thus form
what are called continuous lines of fortification.

With regard to the nature of the fortified supporting points. Nature of
strong earthworks require much time and many men for their ■^ppprtiiig
construction, fumis^h very little fire in comparison to the labour
expended, and do not admit of obstinate defence until completed.
For these reasons the defensible localities before mentioned
are generally to be preferred to them, provided they are favour-
ably situated and do not require too large garrisons ; no time,
however short, need be lU-expended in their pre[)aration, and
every additional hour's work renders them stronger. The de-
fenders, however, being more scattered, unity of action is more
diflScult.

114. The governing line of the trace in field fortification is that
from which the fire proceeds; viz., in earthworks, the interior
crest of the parapet.

The trace of single works depends upon the directions in Tivceofnqgle
which they are required to throw their fire ; they may have ^o*»«
to do this all round, over any portion of the circle, or in special
directions only, according to their position with respect to other
neiglibouring works, Le,y according to the extent of their exposure
to the enemy's artillery fire. Those which are exposed to the
latter on every side require equally thick parapets throughout,
and are called closed works. Glofled works.

Those which are not exposed to fire all round need only have Open works,
thick parapets on the exposed side, and the rear may be left quite
open, in which case they are called open works ; or, the
opening may be closed by a slight earthen parapet or stockailing,
or by obstacles only, in which case they are called half-closed Half-dosed
works. * ^^^•-

70 ELElfENTABT FIELD FOBTIFICATIOK.

Use of cloeed Closed works are only suitable for isolated sitaationB, or for the
works. flanks of a line, or as reserve works.

Use of open Open works are only suitable to situations in which natural

works. obstacles near them render them safe from capture by the rear;

or when their garrisons^ after delivering their fire under cover,
are not intended to wait to be surrounded, but to retire on tbe
near approach of the enemy^ leaving the interior open to the
infantry and artillery fire of works or troops in rear.
Use of half- Half -closed works are used when the works are liable to sur-

closed works, p^j^^ ^^ attack in rear by infantry only. Obstacles may be

sufficient against surprise ; but against infantry attack a limber
stockade {see paragraph 118) or thin earthen parapet is necessary.
This will not interfere^ in case of capture, with the fire of artillery
from positions in rear.
Gorge. The unexposed side of a field work is called the gorge.

Faces. The enclosing straight lines and parapets are osdled faces,

and those faces which are especially traced so as to furnish flank-
Flanks, ing fire are called ^anA«.

Salients. Angles projecting outwards towards the enemy are called iolM

angles ; those projecting inwards are called re-entering angles*

The following are the main rules to be observed : —
Rales of trace. (a.) The trace should be as simple as possible, with few
For fire effect faces, and giving powerful direct fire on the side most liable to

attack. For effective fire the faces should be^ as nearly as possible,
perpendicular to the direction in which they are to fire. A small
deviation may be allowed on either side of the perpendicular; at
the outside 30° for ordinary faces^ and for fianks not more than
lO"". This would allow salient angles of 120° without any great
sacrifice of direct fire. (Fig. 3, PI. XV.)

(ft.) The length of the crest line and the interior space should
be proportioned to the number of men in the garrison.

(c.) Flanks must be within effective range of the farthest point

in the line they are intended to flank, viz., 400 yar^s to 600 yards

for rifles, and 1,500 to 2,000 yards for guns. They ought not to

be less than 10 yards long.

For coYCP. (d.) The faces must not be easily enfiladed, especially those

bearing directly on the attack ; to this end, their prolongations
should, if possible, fall on the ground in or near the defenders* line*
or on marshy or other ground unfavourable for the enemy s
batteries.

(^.) Sharp salient angles should be avoided. They must not
be less than 60°. The more acute the angle the more divergent
the fire of the faces forming it (Fig. 3, PI. XV.), and consequently
the worse defended the capital, (The capital is an imaginary
line bisecting a salient.) Very acute salients, moreover, restnc
the interior space, not allowing room for the free working of gnns >
they also weaken the earthwork for resisting fire.

(/.) Enclosed works should be made of small depth towar^^
the enemy, in order to avoid as much as possible the damaging
effects of his fire.

F.F. Plate X7.

fa.)

TRACE OF FIELD IfORKS.

.ACTIVE. . Fia 1 PASSIVE

/ . I*

(f>)

^ /Shooting Luu> ^

Jteservu. ■"■

Supports

" Svippaits

RBserre

Fig.Z.

Pitf.4.

-•»:-

,-r

^...

Fig 5.

Fuf6

^::^

7^.7

Offp LoPagf 71.

D«j)?,crfi-a<1 ?2Bedfoi-l T* f o-«ij«. 'iti^ea

FIELD WORKS'. 71

Irregularities of the ground yerj often make it much easier
to avoid the effects of enfilade and reverse fire ; but when all
these e;^pedient8 fail^ recourse must be had to shot-proof mounds,
called traverses or parados^ or to other methods hereafter described.
{See paragraphs 129 and 141.)

115. Works take different names^ according to the number of j^^"?** '^^"^
exposed faces they have.

A single line of parapet, only firing in one directioUi and having a stngle line,
its flanks exposed, is only suited to barring intervals between other
works, or to sweeping defiles or narrow passes when the flanks
are unassailable.

Shelter trenches are made generally in this form, as they are
not applied as a rule to situations where great defensive strength
is required, but only to cover the shooting hoe. (Figs. 1, 2, PLXV.)

In a work having two faces, they may make any angle greater Two ndet.
than 60^. This is called a Jfl6cke or redan ; it is chiefly used ^^^l^
as an intermediate work, flanking others to the right and left
Bedans are also suitable for advanced works, or to cover a bridge,
when flanked by the close fire of others in rear. (Fig. 3.)

Works having three faces are used when front and flank fire Time aidet^
are required, chiefly as intermediate works in retired situations. ^ ^ ^^*
They are called blunted redans. (Fig. 4.)

Works having four faces are used for distributing fire over the Four ndet.
front and at the same time affording flanking flre. They are ^^^^^
called lunettes. This is a very usual form for the supporting
points in a line. A blunt salient angle (not less than 120^ is
the best. (Fig. 5.)

Works having five faces {blunted lunettes) are suitable for Fire stdes.
sweeping the greater part of the circle (|- to |), and are applicable ^^^ ^^^
to advanced positions of importance. Ordinary open works would
not have more than five faces. (Fig. 6.)

The gorge of half-closed works is usually closed either by Gorge,
a parapet or stockade, made strught as in Fig. 5, or slightly
projecting (Fig. 4), or re-entering (Kg. 6), according to the
chiuracter of the work ; the closing stockade or parapet is usually
flanked by a small redan, or a tambour {see para. 122), and is
subject to the same rules regarding enfilade as other face& The
faces of the flanking redan or tambour ought to be long enough
to give room for at least half a dozen rifles (say 5 yards to
15 yards) ; its salient should be, like all others, not less than 60^.

Closed works of polygonal form would not usually have more Closed works,
sides than six (Fig. 7), (this leaves no undefended sdients, if 30^
deviation of fire from the perpendicular be conceded,) and never
less than four. The latter is the simplest form, and well suited,
notwithstanding the weakness of its salients, to hasty works and
ix) those holding small garrisons. (Fig. 1, PI. XVI.)

116. None of the above works are capable of defending their
own ditches from the parapet, and the term redoubt is often
applied to all closed or half-closed works of this class. This defect '
is not considered a very great one in ordinary field fortification,
as small ditches are not in reality very serious obstacles, and

72 ELBMBXTARY FXKLO FORTIFIOATIOK.

woald probably not justify tbe extra time and labour involved in

flanking expedients.
Independent If, in lar^e works of much importance^ it should be required to

flanking trace, fl^nk the ditches, this must be done either by breaking the parapet

into re-entering angles, or by placing in the ditch small covered

wooden galleries to hold riflemen. The construction of these

galleries is described in paragraph 125.

Flanking from Of the various modes of modifying the trace of the parapet
the parapets, fo,. independent flank defence^ comes first in order the tenaille
Tenaille trace, irace, which merely consists in alternate silent and re-entering

angles, the fsices flanking one another ; to do this thoroughly the
re-entering angles must not be greater than 120*^ (better not
greater than 100**). The chief defects of an arrangement of this
sort are a certain sacrifice of frontal fire ; greater liability to
enfilade and reverse fire ; restriction of interior .space (ee«pecially
in the case of lines enclosing a small area) ; and imperfect defence
of the ditch at the re-entering angles, producing what are termed
dead angles. Fig. 6, PI. XVI., explains more clearly the
meaning of this term.

Star trace. When the tenaille trace is applied to a complete circle, it

produces what is generally known as the star trace (Fig. 5,
PL XVI.), in which the defects above mentioned are seen in
the highest degree.

Bastioned A more perfect flank defence, involving less sharp salients, may

trace. |jg obtained by a further modification, known as the bastioned

trace^ in which short special flanks are made to bring a cross-
fire on the ground in front of the salients, and to defend the
ditches. The trace may be applied to any polygbn, provided that
none of its angles are less than 90**, in which case the salient
resulting from this particular construction would be too acute.
In Fig. 2, which expkins the technical names of the various parts,
the trace has been applied to a square ; the lunettes at the
salients are the bastions^ and their inner ends are connected by
lines of parapet called curtains.

The flanks of a front (the portion included between any twa
adjacent salients) should be sufliciently far apart to prevent any
dead space from occurring in the ditch of the curtain between
them.

If the ditch of a front follows at a uniform distance tb^
contortions of the parapet (a usual but by no means imperative
condition), it is evident that without some special arrangement
there will be dead space in the ditches of the flanks as wdl as m
those of the faces of the bastions near the angles of the shoulder.

Of the methods of wholly or partially remedying this defect,
three may be noticed, the simplest being that shown in Fig- ^i
PI. XVI., in which the ditches of the faces are carried on straight
and ramped or sloped at the ends in such a^way as to be swept
* by the fire of the flanks ; this still leaves dead space in the ditches
oi the flanks, unless (as shown in Fig. 4), the latter are omitted
altogether and replaced by other obstacles, in which case the

]SipianiFuf.S, f ' I

F.F.HaieXVr.
TRAld! OF FIKLU WORKS.

■r.^r .Si.l,

■1Tnd^f,idr4'^:.'>

V ' "•"""■

FaiYiitHumiiii /*■ / lirtrrur SiJr

Fiff ;t.

Shtrh tUu.<iiratiity iff
ammyanrrU oC loantergearp

FIELD WOBKS. 73

eaHh for their parapets would have to be obtained from a trench
an rear.

In Fig. 3 a better^ but more elaborate arrangement ia shown :
here it has not been considered necessary to defend the ditches
•of the flanks closer than to within 3 ft of the bottom.

The thiixl method is very laborious, and consists in excavating
to the depth of the ditches the whole of the earth between the
counterscarps of the ditches of the faces produced, and the escarps
of the flanks and curtain ; this method is applied to permanent
works, but is generally unsuited to field works.

The bastioned trace is very seldom used, on account of its Basdooed
complicated construction, its inapplicability to very irregular *"**•
ground, and the loss of direct deience at the salients ; it is not
suited to a shorter exterior side than 120 yards, nor would a
longer than 240 yards be likely to be required in field fortification.

In the example given it will be seen that the angle of the
original square on which it is formed is much reduced, and the
^lefence of the capital of the bastion weakened thereby. Other Other self-
self-flanking traces have been constructed, but all have the same ^I^^ing tncet.
objections, complexity and sacrifice of frontal fire.

Works the parapets of which flank the ditches are called forts. Forts,
in contradistinction to redoubts.

In field fortification it is better to obtain good frontal fire, to
make the ditches as impassable as possible by obstacles, and to
leave tlie defence of the ground in front of necessarily acute
salients to adjacent works or troops in position ; this last is much
favoured by the long range of modem weapons. Fig. 4 (a),
PI. XXXIII., shows how obstacles may be used to strengthen the
ground in front of weak salients.

Size and Garrison of Works.

117. The size of works depends generally on the troops that Sise of works,
can be spared to garrison them, but sometimes on the particular
form of the ground, which may require a certain extent of parapet
to sweep it with fire.

The garrison of field redoubts should always consist of some GuTisoa.
tactical unit or units, varying from a company to a battalion.
YiUages and other improvised supporting points may require from
half a battalion to three battalions according to size.

The distribution of men may be ordinarily reckoned as follows :— Distribution of
One man to every pace of crest line, as a shooting line. ™®"'

Half as many at the foot of the banquette, or in the rear

trench, as supports and to replace casualties.
In addition, i to ^ of the whole garrison as a reserve in the

interior, to charge the enemy if he penetrates.

In making rough calculations, two men per pace may be allowed
all round, including reserves. In very isolated situations the
garrison may be three men per pace including reserves.

It is not as a rule advisable to place guns in works, as their Artillery.
mobility is lost, and they may be silenced by the heavy &e which

42642. T

ELEMENTABT FIELD FOBTIFIOATION,

Namber of
gans.

Space.

usually precedes the assault of the works. It is usual, however,
to adapt certain portions of the parapet (chiefly at the salients,
where the field of fire is the greatest) for the use of guns, in case
they should be required.

The number of guns would not usually be greater than 12, and
never less than two. Gatlings are especially useful for firing
alon^ weakly-defended capitals, and for flanking fire.

No allowance need be made for guns mounted en barbette,
(see para. 131), as this does not prevent infantry from using the
parapet when the guns are withdrawn ; but otherwise, a deduction
of 15 feet (six paces) should be made for each gun from the space
available for infantry.
Interior space. As a rule the garrisons of field redoubts would not live inside

them, but a guard would be detailed until occupation for defence
were necessary. If, as in isolated situations, the garrison has to
live inside, a sufficiency of space is given by the following rule :—

For each man, 15 sq. feet (minimum).

„ gun, inclusive of gunners, &c., 600 sq. feet,
a traverse, to cover the entrance, say 1,000 sq. feet

These amounts should be less than the total area included within
the crest line.

The above conditions determine the size of worksj 2.^., the total
length of crest line, and this must be distributed amongst the faces
according to the importance of the fire they have to furnish.

Flanks should never be less than 10 yards long for infantry
defence only. If guns are provided for, not less than 25 yards.

To find the length of crest line of a field redoubt, to be held by
a force of four companies of. infantry, and three guns ; one company
in reserve.

Men firing and in support = | x 400 = 300 ; of these one
third are in support.

.'. number of men firing = f x 300 = 200
crest line = 200 paces = f x 200 yards =166 yards.

No addition need be made for guns, which may here be con-
sidered as mounted en barbette.

This space to be distributed amongst the faces of work accord-
ing to circumstances.

With one fourth in reserve, it will be seen that the result
obtained above exactly agre es with the general rule of two men
per pace ; for in this case the number of paces = ^ = 200.

Flanks.

Example.

Stockades.

Section 7. — ^Details of Field Wobks.

Stockades*

118. Where timber is plentiful, stockades may be made, as
already mentioned, to close the gorges of works, or in other posi-
tions where they will not be exposed to artillery fire, and where
troops are acting purely on the defensive.

Stockades are usually constructed by planting one or more rows
•of timbers upright, and close to one another so as to keep out

jiir

LOOPHOLES.

Fig.il

r-r r

OaUtdi fntuh

Ptgtt J.

W' '.11 II q

Opp U'J'agt IS

DETAILS OF FIELD WOBXS. 75

rifle bullets. Loopholes are ikiade at intervals^ usually of not less
than 2 ft. 6 in. (Men can» if need be, fire at 2-feet intervals.)

The timbers are usually from 6 ins. to 14 ins. thick, or in
diameter, 10 to 15 feet long (pointed at top or fitted with iron
spikes if there is time) ; they are sunk 3 or 4 feet in the ground.
A riband may be spiked to the timbers to keep them together on
the inside ; near the top sawyers dogs may be also freely used to
keep the timbers together.

The loopholes in stockades should be so placed that the enemy LoopholM io
shall not be able to use them if he doses on the stockade, and for ■^<>c*«^***
this reason they should be at least 6 feet above the ground on the
outside (Figs. 1, 2, 3, PL XVII.) ; there must, therefore, either be
a banquette on the inside (Fig. 2), or a ditch on the outside
(Fig. 1), or there must be some obstacle to prevent the enemy firom
coming dose up to the stockade.

A small ditch on the outside furnishes earth, which can be
heaped up against the limbers, making them more impenetrable,
and rendering it more difficult to fix explosives against them.

In order not to weaken the timbers of a stockade in piercing
loopholes through them, it is better to make the loopholes between
two timbers, half being taken out of each.

In stockades of 10 to 12 inches thick the following dimensions DimennoDSy
are oonvenieDt for loopholes; — (Fig. 11, PI. XVII.) *«•

Interior width 9 inches, exterior width 3 inches.
Do. height 12 inches do. height 6 inches.

In round timhers, two saw cuts, as shown in Fig. 12, will make
a loophole.

Loopholes can he iron plated by means of railway chairs and fish
plates, nailed to the outside.

Daylight should not be seen by the enemy through loopholes,
as he can then see when they are occupied by the defenders.

For making the loopholes. Fig. 11 in square timber, the fol-
lowing tools are necessary : — ^2-inch chisel (2 inch), hand-saw, role,
and Itimp of chalk.

One man can cut a loophole in 10 minufces.

The loopholes in Fig. 12 can be cut in 3 minutes with a hand-
saw.

The working party, &c. for making a stockade of square timber Working party
is given below ; it may be taken as a guide for other varieties of for stockade,
stockades. One non-commissioned officer and eight men of in&ntry
with two sappers to guide them. They should erect 15 feet of
stockade in eight hours with one tier of loopholes.

The tools necessary are — Tools.

Shovels • - - 2

Axes, pick - - 2

Rope, H inches - 5 fathoms

Rammers - - 2

Handspikes - - 2

Chisels, 2-in. - - 2

Crowbar - - - 1

Saws, hand - * ^ I Dogs, sawyers, are useful 20

Two men dig the trench 3 to 4 feet deep, and about a foot or
18 inches wide. Two men under one sapper are set to work with

F 2

Saws, cross-cut • • 1

Rod, measuring 6 feet - 1

Tape, 50 feet - - 1

Lines, tracing - - 1

Spikes, 8-in. - - 30

Hammers, 4 lb. - - 1

Mallets - - - 2

ELEM£NTABY FIELD POKTIFIOATION.

Varieties of
stockades.

Fascine
-stockades.

Railway bar
stockades.

the cross-cut saw to regulate the length of timbers. Two men
under one of the sappers are put to cut the loopholes.

When the timbers have been cut to length, the loopholes pierced,
and the trench is completed, the whole parbr are employed at
carrying the baulks and erecting the stockade, by means of the
two handspikes and coil of rope, dogging up each timber as it is
put in placie.

One sapper looks after the baulks being brought up in regular
order, and sees that the men lift the loads and work together ; the
other sapper adjusts the stockade by means of the crowbar, and
dogs up, and spikes on the ribands as the work progresses.

Examples of stockadiBg of various kinds, showing different
modes of arranging the timbers according to whether they are
square or round, stout or slender, are given in Figs. 5, 6, 7, 8,
PI. XVII.

Pig. 4, PI. XVII., shows a method of arranging squared
timbers when time does not permit of loopholes being cut ; the
cover, however, is imperfect.

With round timbers, straight trees such as fir are the best for
the purpose; they should be squared where they touch (Fig. 6):
if there is not time for this, or if the trees are not very straight,
the junctions of every two trees must be covered by a second row
in rear (Figs. 6, 7, 8), or if necessary by rows both in front and
rear.

These intermediate timbers must be cut off to a height of about
4 feet above the ground, or banquettes made where the loop-
holes, or intervals for firing through, exist (Figs. 6, 7, 8).

Fig. 9 is a method of arranging half timbers, such as are
frequently found stacked as railway sleepers.

Fig. 10 shows the treatment for quarter timbers.

The tops of timbers may be cut off straight, and large nails
driven in to increase the difficulty of getting over the stockade
(Fi^. 7).

Fig. 3 shows a high stockade regulated for two tiers of loop-
holes; the trench shown by dotted lines may be substituted
for that shown in sketch, to admit of men firing from the knee
instead of in the lying position.

119. Fascines in two or three rows sunk 4 to 5 feet in the
ground and strutted back, make a very excellent stockade;
horizontal ribands of hop-poles or light timber tied together with
wire are required to keep the fascines together, and some struts
about 8 feet apart well secured into the earth in rear, fastened to
two of. the ribands, add stiffiiess to the structure (Figs. 1, 2,
PI. XVIII.). Similar stockades can be made of bundles of
bamboos.

Brushwood loopholes work in well in this sort of stockade, or
else rough splayed boxes of inch plunk will answer.

It is very difficult indeed to blow down a fascine stockade ; gun
cotton except in very large charges will not destroy it ; powder
has a better effect on it. It is even difficult to demolish this
stockade with artillery fire.

120. If railway plant is at hand it will be found very useful
for stockades.

FF, pinu-.iyin

VARIOUS KINDS OF ST0(:K,U)KS.

OUN AND &ATUNG PORTS.

Ctiui or Oatliii^-port in, Sie<kadM .

,?ff|is™«'ir

iMule 1 tem/Z4>n, ""^^ Arou^h Gan-Fort.

O itiwui - Pat in, Rail Sfoehad^.

DETAILS OP FIELD WORKS. 77

Kg. 3, PL XIX., and Fig. 5, PI. XVIII,, show stockades made
altogether of rails.

Sleepers and rails can also be worked together to innke a very
strong stockade (Figs. 3, 4, 6, PI. XVlII.). This sort of
stockades is more applicable where only a short length of
obstacle is wanted, as they require a groat deal of plant ; they
are suitable for covering guns and Oatlings, or closing a road, ana
are more properly barriers.

121. Gun ports can be cut in stockades for field guns and Gun ports.
Gatling guns^ (Fig. 1, 2, PI. XIX). They should be about

1 foot 6 in. wide and 2 fl. high, and 3 ft. 3 in. above the ground.

Breastworks may be formed of a row of weak timbers Bx^tstworics.
strengthened by earth to the height of a man's breast, retained by
means of planks and stakes, or hurdles tied back with wire to the
upright posts (Fig. 5, PI. XIX.).

Fascines and logs laid horizontally between posts or railway
bars also make a good breastwork. (Figs. 6, 7, ^L XIX.)

Tambours,

122. For giving flanking fire in the front of stockades and Tsmbonrs*
walls projections may be thrown out of triangular or rectangular

shape called tambours.

Tambours should be pierced with loopholes for as many men as
can conveniently fire out of them. When practicable they should
be covered to make them splinter proof They are well placed
at the sides of passages or entrances through walls or stockades,
and may even be used in front of these openingz). (Figs. 6, 7,
PL XI.)

In flanking a long line by tambours, they should be arranged so
as not to fire into each other. The retreat from them should also
be well protected, as they have to be held to the last moment, when
an enemy has got close to the work they are intended to defend.
A covered trench from the interior of the tambour for some dis-
tance to the rear will give protection to the retreat of the
defenders. (Fig. 7, PL XI.).

Blindages, Sfc,

123. Structures intended to give overhead shelter to men or guns
against artillery fire are variously called blindages, field casemates,
and splinter proofs. The last term is generally applied to the
slighter forms of cover to protect from splinters of shells, and the
term field casemates to detached structures for covering piquet*
guards, supports, &c.

Floor space should be allowed at the rate of ^ square yard per
man for troops crowded together ; and 2 yards per man when
intended for occupation, as by guards or picquets.

A covering of logs or baulks, 10 to 12 inches thick, railway
bars, or two or three tiers of &scines, with 4 or 5 feet of earth
over them, are proof against common shell from field guns.

•78

ELEMENTARY FIELD FORTIFICATION.

Working
party.

Tools and
materials for a
casemate.

The entrances can be by steps or ramps, either at intervab or
the whole length ; the latter is the best plan when they are in the
front line of an intrenched position, to prevent an enemy gaining
tmy cover against interior lines should he gain possession of the
casemate.

Blindages in field works can be constructed either during the
progress of the work of throwing up a parapet^ or after its com-
pretion. Fig 2, PI. XX.^ gives an example of the former system,
and Fig. 1, PI. XX., of the latter.

Detached casemates for supports, reserves, and garrisons of
posts are shown in Figs. 3 and 4, PI. XX.

Fifty feet or 20 paces of tlie casemate. Fig. 3, can be made in
eight bours with the following detail of men, tools, and
material : —

One non-commissioned officer of Royal Engineers and six

sappers.
One non-commissioned officer and 40 men of infantiy, and one
sapper.

r20 men digging in main trench, at two paces apart,
1st relief, | in two lines,

four. -^ 10 men filling sand bags,
hours. J 10 men, with four sappers cutting and carrying

L timber.
2nd relief : —

15 men fixing fi*ames and revetting roof (with four sappers).
15 men shovelling on to roof, with o^e sapper.
10 men diggjing slope in rear, with one sapper, and throwing
earth on top.
This distribution of working parties for the various examples of
casemates can be varied according to the nature of soil and
materials used, and the time available for the work.

.The tools and stores for the casemate in Fig. 3, PI. XX., for the
party above detailed are as follows : —
For 50 feet of casemate : —

Timbers or baulks, 10 inches
diameter or square.

Dogs, sawyers
8-in. spikes
Sandbags -

60 roof beams

8 bearers
18 uprights

9 scruts -

12 feet long.
12 feet long.

6 feet long.

9 feet long.

60
500

Axes, pick
Saws, nand
Augurs, 1 inch -
Gimlets, i inch -
Chisels, 2 inch
Rod, measuring, 6 inch
Rules, 2 feet

Shovels -
Saws, cross-cut -
Hammers, 4 lb. -
Adzes
Mallets -
Tape, 50 feet

- 30

- 2

- 4
. 2
. 2

- 1
. 1

Sheeting 2 inches, 300 feet super, or 20 fascines 18 feet long
Tools for each relief : —

- 20

- 4

- 2
. 2

1 I Lines (100 feet) -
A casemate similar to the one described, but covered with rail-
way bars and two feet of earth, is shown in Fig. 4, PI. XX. ; much
the same workinff party and tools are required, and the time for
construction will be about the same.

Other examples of blinded cover are given in Plate XXI.
Splinterproofs. Splinter proofs can be made of almost any materials: they

should be placed on the reverse side of banks^ walls, or parapets
(that is, the side away from the enemy's fire) ; usually they are
made as lean-to structures. Planks or fascines with a foot of

F.F.Pl«u..\X.

U 1. 1 .\ |).\(. I-. S

Kfl

r br CBiifevclid at jjpM&n

^^ awi -wr

"■ \ //'

X/:

1 a^iu^ ^ 1 ^^uU

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J \mmmtnnmSl. '"" r.'.

F.F.i'i«uM:m._

PLATFOIIAIS. MAC.A/lNKS.,C,APOWIBRS.

DETAILS OF FIBLD WOBX8. 79

earth oyer them^ and rails, or timbers about 6 inches round or
square, are proof against splinters of shells or shrapnel bullets.

An example is given of a splinter proof against a bank as coyer
for supports and reserves in Figs. 1, 2, 3, PI. XXL ; it would
take about 6 to 8 hours to make.

124. Blindages for guns and Gatlings are given in Fig. 4, Blindages for

PL XXI. and in PL XXII. gJJ^^

The Gailing blindage has been made to fire from, and takes 10 ^'

or 12 men about four hours to throw up.

For guns the dimensions should be 10 feet by 15 feet, the
working party doubled to 20 men, and eight hours given for
construction.

The blindages for firing from are specially applicable to guns
and Gatlings placed in positions for the purposes of flank defence.
(Fig. 4, PI. XXI.)

In the description of defence of walls it was mentioned that
Gatlings should flank ditches and sweep the ground in front of
the walls. In such cases they should be placed in the blindages
here mentioned.

The blindage for a gun and limber (Plate XXII.) may be
made to answer for two guns. It is erected on the interior slope
of a parapet 8 feet high, and shows how the gun can be kept
covered till the moment it is required for close ranges to resist
a developed attack.

If guns were kept in position en barbette in a front line of
defence or in a redoubt tney would probably be dismounted^ but
by giving good cover to them in such situations^ they are effective
at the critical moment when an enemy is near the line of defences^
and when his own artillery cannot support him.

Caponiers, <fcc.

125. Caponiers, to flank ditches, are usually constructed at the Caponiers,
salients. They must be placed so as to be sheltered from artil- I*o6ition.
lery fire, and to help this object the roof should be kept as low as
possible. Fig. 3, PI. XXIII., shows their application to a lunette.
They must be either entered from the interior of the work by
galleries, or from the ditch through doors ; the former method is
much to be preferred, as in the latter the men in them may be
cut off.

As a means of defence they do not repay the labour of con-
struction, except in large deliberately constructed works, with
deep ditches presenting a Eerious obstacle to assault.

Fig. 7, PL XXIII., gives an example- of a caponier at the
salient of a work, to flank the two ditches of the faces.

The walls are usually constructed of stockading, on which is Construction.
laid a roof of earth supported by logs or rails.

As in ordinary stockades, the loopholes should be constructed
so as not to be used by the enemy. Figs, 7 and 8, PI. XXIII.,
are examples. The minimum width for a caponier firing both

ELKMEKTABY FIELD FOBTIFICATION.

Escarp and

counterscarp

galleries.

waye i8 8 ft., that for a siDgle caponier (as at the shoulder of a
lunette) is 4 ft. 6 in.

For the construction of the galleries to caponiers, see the
chapter on mining.

126. Escarp and counterscarp galleries may be applied tO'
re-entering angles of either the escarp or counterscarp; their
construction is similar to that of caponiers.

The two faces of one gallery may be made to sweep two ditche»
and mutually to flank one another. The entrance to a counter-
scarp gallery is usually by a door into the ditch, and thence by a
gallery into the work ; or in large works there may be a gallery
under the ditch into the work. They are open to the same
objection for use in field works as are caponiers.

Fig. 9, PI. XXIII., gives the plan of an escarp gallery, con-
structed without cutting away any of the escarp.

Keep or reduit.

Retrenchment^ Keep, or Reduit

127* Large fieldworks having plenty of interior space may be

enabled to protract their resistance by means of a second enclosure

within the outer line of parapet. Tnis is called a retrenchment,

keep, or reduit.

Ketrenchmeut. A retrenchment is a line of parapet separating a large work

into two parts. It must see into all parts of the cut-off portion,
with which it is connected by well-defended passages. This forms
a second line of defence in case of the failure of the first.

A keep or reduit is a separate enclosure within the outer
inclosure, seeing into all parts of the latter, having a greater
command if possible, and a separate garrison for its defence
(Figs. 3, 4, PL XXIV.) ; it forces the assailants to conmience the
fight anew, and gains time for the retreat of ' the garrison or for
the arrival of assistance fVom without. The entrance to the main
work must not pass through the keep.

The keep, in lunettes with light gorges, is usually placed so that
the gorge tambour may form a part of it. (Fig. 2, PL XXI 7.)

It would not as a rule be worth making a keep unless a com-
pany or more could be spared for its garrison, i,f\, unless the whole
garrison of the work were half a battalion or more.

If the front parapets of a work have a good command, and the
terreplein is on a reverse slope of a hill, so that the keep is fairly
sheltered from fire, a stockaded enclosure (Fig. 6, PI. XXIV.),
which is economical in interior space, may serve the purpose^
In large works, or when the keep is required to resist artillery,
it should be enclosed in front by earthen parapets, having ditches
if interior space is abundant (Fig. 6) ; but otherwise, the base
of the exterior slope must b^ strewn with obstacles which do not
take up much room,

Instead of the exterior slope the parapet may be revetted nearly
perpendicularly with strong stockade work.

Therei should be blinded cover in the keep, under the front
parapet,

Position of
keep.

Garrison.

Construction.

Esca
cour
gal)

DETAILS OF FIELD WORKS. 81

Blockhouses may be applied as keeps to field works ; they are
described in paragraph 134.

JSntrances.

128. The entrance to a field work should be on the least Fodtion.
exposed side^ usually at the gorge, and if possible, under close
flanking fire.

The width of passage requisite for infimtry is 4 feet ; for Width,
artillery^ 7 feet in the clear. The narrower the opening the
better ; the sides of a passage through an earthen parapet should,
therefore, be revetted to stand at as steep a slope as possible. As
a rule, artillery fire need not be expected on the side where the
entrance is placed, and loop-holed bullet-proof gates will generally Bullet-proof
suflSce when there is time to make them. They should open out- ^^*
wards (Fig. 1, PL XXV.) and be double hung when over 4 feet
wide.

Fig. 2 shows a gate for infantry through a line of palisades^ Swing barrier,
composed of a single leaf of five palisades^ turning on a central
pivot.

Fig. 3 shows a bullet-proof moveable barrier composed of baulks
slipped successively into side grooves.

Small ditches can be crossed either by planks^ or by leaving a
piece of the natural ground 10 feet wide opposite the entrance^ as
in Fig. 1, PI. XXIV.

Larger ditches require bridges of baulks and planking, which
can be made to remove entirely^ if not very wide ; or the nearest
10 feet to the work may be made to draw back into the work.

Fig. 4, PI. XXXVI., gives a sketch of a trestle bridge of the
latter description.

Traverses,

129. On lines, of parapet unavoidably exposed to enfilade fire, TraverseB.
traverses are required. These are usually made of earthy the side

which receives the enemy's shot sloping ^ and the unexposed sides
being revetted to stand at slopes of |- to -f-^ to save space. Their
thickness must usually be the same as that of the parapet^ as they
have to resist the same fire. The height must vary according to
the amount of protection required in rear of them.

The top is usually formed into a ridge with gentle slopes of
about -^ to carry off the rain water. The length must be suf-
ficient to cover the banquette and rear trench in order to protect
infantry ; and at least 20 feet (measured from the crest of the
parapet) to protect guns. Fig. 4, PL XXVIII., gives a traverse of
this description.

Traverses may also be required to protect the backs of men
using parapets that may be taken in reverse^ in which case they
are called *' parados."

Large traverses are sometimes required to conceal the interior
of works in exposed situations. The rules governing their form
are given under the heading of defilade, para. 141.

ELEMEKTABY FIELD FORTIFICATION*

When an entrance is exposed to artillerj fire an earthen
traverse inside becomes necessary. (Fig. 5, PI. XXV.)

The traverse should be of the same profile as the parapet^
and between it and the banquette there should only be the width
necessary for the roadway ; the slope of tbe banquette should be
cut off at an angle of 45^ in plan^ to facilitate die guns turning
the angle. The length of the traverse will depend upon the width
of the opening and the thickness of the parapet ; in Ilg. 5 its
length towards the left has beeii diminished by making the parapet
at the angle extend over the tread of the banquette.

The dotted lines (Fig. 6, PI. XXV.) represent lines of fire
passing through the opening, in the most oblique direction possible,
at 4^ feet above and parallel to the ground. The line of fire
represented by a ft in plan grazes the exterior slope at c, the
interior slope at d, and strikes the traverse at b ; again, the line of
fire represented by e^* grazes the exterior slope at /, the revetment
of the parapet at g, and strikes the traverse at/; it will be seen
that owing to the parapet on the left having been thickened^ A /is
7^ feet less than h b. The traverse should be made to extend
4 feet further than tlje points b and /, and being for defence, is
shown with a banquette, the portion opposite the opening being
arranged for a double rank. When the entrance is placed at a re-
entering angles the traverse is often connected with the parapet as
shown by the dotted lines ; the line of fire ejf will in this case be
determined by the points k and ff^ if k lies outside the prolongation

0{ffl.

A musket-proof traverse to cover an entrance may be made of
stockading (Fig. 1, PI. XXIV.).

Splinter-proof traverses are used between guns on a line of
parapet, subject only to direct fire. They prevent the effects of
bursting shells extending to more than one gun division.

Means provided for Artillery.

130. The height of the axis of a 16-pr. gun in our service is
3 feet 7^ inches. For direct fire, therefore, the parapet it fires
over should not exceed 3^ feet in height above the ground on
which the wheels stand.

Embrasures weaken the parapet, give a very limited lateral
range, form a good mark for the enemy, and require frequent
repair, from the difficulty of revetting the sides so as to stand
the explosion of the gun for any length of time. The use of
deep embrasures should therefore be confined to flanks and
other places not exposed to direct fire, and where Ijut little lateral
range is required.
Confltruction. Two adjoining embrasures should not be nearer than 16 feet

from centre to centre, both to allow space for working the guns,
and in order that the merlon or parapet between them should
not be so weak as to be easily destroyed by shells ; 20 feet is better
when space admits of it.

Embrasures for guns firing at high angles may be made
countersloping, which improves the cover (Fig. 1, Plate XXVL)*

Splinter-proof
traverses.

Embrasares.
Defects.

F.F.FUJpHV. _ _
BARRIERS - TRAVE RS li: 8 .

1 , rnlttaduig, rrrliml l\rat

•.ml- -JO tl to lutti,..

EMBHAStTRES.

Secbtn aLk . _ dftr thaK 1 it

, FtaHi Of \m. tf«^j

TlttBER • EHRTH BLIND SuCUoll

DETAILS OF FIELD WOKK8. 83

The interior opening or neck of embrasures intended for direct Constmctlon.
fire should be as small as possible. A width of 2 ft is sufficient for For direct fire,
field guns. The bottom or sole must admit of the gun being
depressed as much as may be required ; ordinarily a slope of ^
to the front will be sufficient to provide for drainage.

The amount of splay which is given to the sole depends on
the lateral range required. It is usual to make this not less than
■^ on each side of the central line or axis of the embrasure^ to
guard against the effects of the explosion of the gun ; it is not
advisable to give a greater splay than -^ on each side (giving a
lateral range of about 20°), as the embrasure would become too
weak at the neck.

The sides or cheeks are made with a winding slope ; steep
(|- to ^) at the neck to diminish the exposure of the gunners,
and gradually flattening out to about -^ at the external opening or
mouth to diminish the destructive effects of the explosion, and
also because the outer portion, being more likely to be struck by
shells, mu8t.be left at the natural slope of the earth. The cheeks
must be revetted for about 8 to 10 feet from the neck by one of
the methods explained later in the chapter on Siege Works.

When an embrasure is made counter sloping ^ for indirect fire For indirect
only, the sill (or inner edge of the sole) noay be made 6 inches ^"*
higher as the piece is elevated, and the sole slopes towards the
iiiterior of the work at the angle of minimum elevation required,
provided that if the gun is to be actually laid on the object the
line of sight be clear. The latter will be mostly ensured if the
height of the sole at the mouth is not greater than 5 feet The
oxposure to the gunners at a countersloping embrasure being so
much less than at an embrasure for direct fire, the cheeks need
not be revetted ; or at any rate they need not be steeper than -f- nt
the neck.

For guns mounted on standing garrison carriages the height of
the ffenouillire (the portion of the interior slope below the sill)
siould not exceed 2' &' ; but as the cheeks at the neck should not
have a greater height than 4 ft., for the sake of stability, it would
be necessary in this case to raise the gim platform : the same
would be the case when the conmiaiid of the parapet exceeded
7«J. feet.

If it should be necessary (in very conunanding situations, for
instance) to provide for much depression, the height of the sill
must be diminished accordingly.

An embrasure should always, if possible, be made with its axis
at right angles to the crest of the parapet. When it is necessary oblique
to make the axis oblique to the crest, the method of construction embrasures,
is the same. Oblique embrasures weaken the parapet more than
the ordinary ones, and do not admit of the muzzle of the gun
being run so far into them. The latter objection is met. by
^^ indenting ^^ the parapet, i.e., by giving the interior crest a saw- indented
like form so that the gun wheels may run close up against it. parapet.
Ii^denting becomes necessary when the axis of the embrasure
makes with the crest an angle less than 80°.

BLEMBNTABY FIELD FORTIFICATIOK.

Blinded em-
brasures.

Gon- banks.

Pan-coup^.

Mantlets. To protect the gunners from rifle bullets entering the embra-

sure, shutters or mantlets should be provided to close the neck.
They may be made of wood, fascines^ iron plate, or rope in two
or three thicknesses, and supported by a frame fixed to the interior
crest. (Figs. 2, 3, 4.) ^

Embrasures may be blinded by placing beams of wood or rails
transversely from cheek to cheek, and covering them with fascines
and earth, or earth only. (Fig. 5.)
Barbette fire. 131. In firing over the parapet or en barbette, the gunners are

more exposed, but the lateral range is greater, and there is no
weakening of the parapet Any number of guns may be mounted
alongside one another in this way, either along a straight line of
parapet, or at a salient. The latter is the position usually chosen,
as the field of view is greater. (Pis. XXVII., XXVIII.,|XXIX)

The gunrbanky or surface on which the gun stands, should
be level, and 3^ feet below the crest. Each field-gun requires
along a straight parapet at least 10 feet lineal, measured along
the crest ; 16 feet is the better interval. Guns of position require
18 feet at least. The depth required (measured perpendicular to
the crest) is 20 feet ; but it is desirable to give an additional 4 feet
when there are several guns, for passage room behind them.

A salient angle is usually filled up so as to form a short face, or
" pan-coup^ ^^ about 6 to 15 feet long, in order that half a dozen
rifles, or a gun or Gatling, may fire conveniently along the capital.
The minimum length of the pan-coupe for a gun or Gatling may
be 6 feet.

The sides of the terreplein of gunbanks are usually made with
a slope of \, and it is advisable to leave a small berm 1 foot wide
between the base of these slopes and any excavations near them.
The ramps f or inclined roadways up to them must be 8 ft. wide
at least, and have a slope of ^, or at most i. The sides of the
ramp are made to slope -J-- For three guns or more, two ramps
should be provided. (Fig. 6, 7, PL XXIX.)

The guns in a field work may be overpowered and have to be
withdrawn from the gun-banks until the close attack of the
enemy's infantry, when they must be worked at all hazards. To
protect them from artillery fire it is necessary to bring them under
the close cover of the parapets ; if there is a rear trench it can be
widened near the gun-bank, and ramps of J (7 feet wide for one
gun, 14 feet for two guns), should be made to enable the guns to
be run down into it. To bring the guns closer still to the
parapet a portion of the banquette may be cut away, or the whole
banquette removed for the required width, planks being used for
the infantry to stand on, so as not to lose the fire from that
portion of the parapet. For more complete protection, blindages
may be made, as already mentioned (para. 124).

The exposure of the gunners to riflemen may be greatly
reduced by bonnettes of sandbags, or earth, built up on the
superior slope between the guns.

Gunbanks can be used by infantry ; but if there is time, they
can be made more convenient by forming a small trench 9 in. deep

Ramps.

Gun recesses.

F.F.PUia XXVII.

GUN BANKS

I CUH'EN BARBETTE' ON STRAIGHT PARAPET - 2 RELIEFS

r»i o > (•or- TASKS)

< so >i

r.v>

Ths Rjetsavaiujrut ^^PP^

Earih/brOuGun

^kmv: Out eaHk^ imdinary
V Ikavipet in (ronl ofCrmi
eomeit dram THteh .

>. i ! / f^lMi^.

ThmtfuufA-

r.A. O***
TUal £ascaMiun^2330 ~ &6 (about)

. IS Do
Bampa \

ThibmBank 4iLtt. u

Total IR . I

'i^f^lUi^. I

n Di^tffmt j

TTTTT/j

I-RELIEF GUN BANK

-J'

SHELL RECESS
Section, on E F .

Opp:io paM

r)auf •!KCLd.d.22.B«^ord S' Co'ent Gfrden.

F.F.HflipXXVIH.

GUN BANKS.

Law GUN BANK loT 3 CUN8.

ofva Strc aghb FkMru4 H4. Fijf ?.

\ J SaiicMf'fAfJ

€mn Bank nvrm ountmuant
ivrRitlMumt .

The Omutn^ Exeavaiion
C^Uiv (km Bunk , <^

'/ Hunuttm-s

Far a, Ei§k(4) Can Bank ahoai- 30 c.ytis
adAHanal wwdtl he reqmr&d ^ to h^
ohiammf, fiviiv Frwvt, Dvtdi .

-tO'6'

OpfttvBa^m.

•:. . '".^i

I'l'*. Vi !v ''f'u'ii iS* "."ent GcLrdaii

DETAILS OF FIELD WORKS. 85

snd 2 ft, broad in the gan-bank all along the interior slope,
revetted with fascines on the side nearest to the gun, to prevent
the gun-wheel from breaking it away (Fig. 2, PI. XXVI 1 1.). In
the construction of gun-banks it is very desirable that as much
earth as possible should be obtained from excavations round them^
as they can be much more quickly made in this way than by
getting the earth from the front ditch. This principle has been
applied totally in the case of those on straight parapets (Figs. 1, 3,
PI. XXYII.) ; but in the case of salients, the extra length of
ditch gives so much surplus of earth that the principle can only
be partially applied.

With salients of 9(f and uuder^ the extra length of ditch will
usually furnish enough earth for the gun-bank for a single gun ;
but when the angle is obtuse the excess is not sufficient, and
the widening of the trench for gun recesses is useful in furnishing
earth.

132. For continuous firing a hard surface is required for the Platforms,
gun to stand on. For this purpose wooden platforms are used, or
planks under the wheels and the trail. The siege ground plat-
form and mode of laying it, is described in the chapter on siege

works. Similar platforms can be made of rough material by *
laying five sleepers of rough sawn timber or flooring joists from
houses and roof timbers, or straight trees (about 5 in. diameter,
each 15 ft. long, as shown in Fig. 2, PI. XXIII.). Across these
may be nailed planks sawn to 10^ ft. lengths.

For firing in one direction only, a very simple arrangement can Plank runuen.
be made with three stout planks, one for the trail and two for
the wheels to run on (Fig. 1, PI. XXIII.). Wedges, or inclined Recoil wedges,
planes, will check the recoil of guns on the principle of ClerVs
platforms.

Magazines.

133. Magazines in field works may be constructed in a similar Magaiines.
manner to those of siege batteries. But in ordinary redoubts

this would take up a great deal of the interior space; it is
generally better to place small magazines, to supply a couple of
guns, somewhere near the pieces, either in the infantry blindages
or splinter-proofs, or in traverses, or under the gun-banks, as near
to the front parapets as possible. They may be either rectangular
or triangular in section (Figs. 4 and 5, PI. XXIII.). They should
have at least 4 feet of earth over their roofs. In sheltered
positions lean-to mngazines may be constructed behind traverses
(Fig. 6, PI. XXIII.).

With one line of wagons each gun has 122 rounds, distributed Quantity of
as follows:— . ammunition.

30 rounds in gun limber.
30 „ wagon limber.
60 „ wagon body.
2 ,> on gun.

ELEHENTABT FIELD FOBTIFICATION.

Ammunition
recesses.

Blockhouses.

Plan.

In field works*
Dimensions.

WallF.

Kailway chair
loopholes.

Entrance.

Walls to resist
artillery.

Two-storied
blockhouses.

For service of guns in works the boxes would be taken off the
limbers and placed in the magazines.

Recesses for limber boxes ^ouid have a height of 2 feet at least
for one row of boxes^ 4 feet 6 inches for two rows, and a width of
4 feet. The depth can be 2 feet for one box, 4 feet for two.
(Pis. XXVII., XXVIII., XXIX.)

Magazines require a minimum headroom of 5 feet, and a width
of 4 feet in the clear.

A magazine for the limber boxes of two guns should have a
floor space of at \eaSst 8 feet by 4 feet (8 feet by 5 feet would be
better).

Blockhouses.

134. Blockhouses are defensible guard-houses or barracks,
having framed or stockaded walls, and roofs of timber or iron rails
with earth on top. They will not stand exposure to artillery
fire, unless specially constructed.

Blockhouses may have any form in plan (Figs. 3, 4, PL XXIV.).
A cruciform plan is very suitable to isolated situations, where they
may be used as detachment guard-houses (Fig. 4, PI. XXXI.).
When used as keeps in field works, they p.hould be kept as low as
possible to protect them firom fire. Whether sunk deep in the
earth, or their fioors kept level with, or above the ground, they
should in any case have the following dimensions : —

Height in the clear, at least 6 feet ; if head-room is not re-
stricted by circumstances, 7^ or 8 feet will make them more airy
and habitable. Minimum width, with one row of beds, 9 feet;
with two rows 15 feet (Fig. 6, PI. XXIV., and Fig. 1, PI. XXX).
The length depends upon the number of guard-beds required,
allowing 2 feet lineal for each man.

The roof should project 2 or 3 feet beyond the walls in order
to give full protection everywhere against curved and high-angle
fire.

The interior of blockhouses should be drained into trenches or
cesspools lower in level than their floors, or the drains should be
led away to low ground. The floor level should not be sunk more
than 4 feet below ground if possible. The walls can either be made
of ordinary stockade-work or of logs laid horizontally and halved
at the corners (Fig. 2, PI. XXX., and Fig. 6, 7, 8, PI. XXIV.),
or they may be of frames and sheeting (Fig. 6, PI. XXIV.).

Fig. 2, PL XXX., gives a section of a blockhouse of speedy
construction, suitable for the interior of field-works.

Railway chairs make very good loopholes for blockhouses, as
shown in Fig. 3, PI. XXX

The entrance may be by a bullet-proof gate, as already described,
or by a moveable barrier.

Resistance to artillery fire is obtained by the use of rails backed
up by stout timbers, as shown in Fig. 2, PI. XXXI., or by wood
only, as in Fig. 1.

Very rarely, and when artillery fire could not be brought to
bear on the building, blockhouses could be made in two storeys,

BLOCKBOUSBS

lift' CT««H«<

IwmI of Ca/ionur ■^--■. '""Tp^ri '=^^1 jf "

^m*- j( epJ hitunj

fiir /"Jiutk DMria:

F.F.rhtexm.

BLOCKHOUSES TO RESIST AKTIU-KltV.

Fig I ' -"

vmoDEH WAILS C., j^ 'j i ^ i ^ ( fcjLjL T J-^-^

s.^,.^, '"^^^^" ■ friiimiJjTr

Fnmt Hlrvatiiin

Jni^ I Ao)

F.F. Plato. XXm. ,

DETAILS OF FIELD WOBK8. 87

the upper of which can be placed diagonally over the lower to
distribute the fire equally all round.

In mountainous and rocky districts, when expoeed to infantry
fire only, excellent defensible guard-houses can be made out of
light frames and sheeting covered by stones built up dry on the
outside and over the roof (Fig. 6, PI. XXX.).

A kind of field caponier or blockhouse can be constructed as
shown in Fig. 4) PL XXX., for flanking lines of wall, &c.

JSxampIes of Field Bedouhts,

185. Plate XXXII. gives two examples of a half-closed
lunette, suitable for one of a chain of fortified pivots.

The right half of the plate has parapets 9 ft. thick, with a light
earthen parapet 3 fit. thick at the gorge. The blindages for the
garrison are such as could be added after the completion of the
rest of the work ; those on the faces are of the section shown
in Fig. 2, PL XX. On the left side of the plate the work is of a
more solid character. The parapets are 12 feet thick and the
gorge is stockaded. The blindages would have to be constructed
at ^e same time as the rest of the work, and have the section
Bhown in Fig. 1, PL XX.

The advantage of a plan which permits of the blindages being
executed after the work is, that the building of the parapets is in
no way interrupted, and they are sooner readv for use. By
giving the parapet a small profile with a ditch not exceeding
60 S.S;. of section, the work could be executed in three reliefs^
and if another relief were available, good casemates could be
added.

The redoubt on the left would take about five reliefs of six
hours each.

The working parties of in&ntry may be reckoned at two men
per pace of the perimeter for each relief.

Sappers to superintend may be reckoned at five p.c. of their
number ; and for constructing blindages sappers wiU be required
at the rate of one man to two yards of blindage for each relief
during which the latter are being constructed.

For a section of a redoubt capable of being constructed in three 3-relief
reliefs, see Fig. 8, PI. XIII. For a hasty work of this kind low redoubt,
gun-banks similar to those in PI. XXVII. should be employed.

In order to admit of rapid construction, such a profile should
be adopted as will allow of excavators being employed for as long
as possible on both sides of \ the parapet, i.e„ the areas of the
ditcn and rear trench must be nearly equal. In such works the
ditch cannot be made in itself a good obstacle.

APPLIED FIELD PORTIPIOATIOK.

CHAPTER III.

•n

LIED FIELD rORTIFlCATION.

Distance of
works in a
single line.

For fire e£fect.

For movement.

Position and
form of works.

Intermediate
works.

Works in two
lines.

Distance from
first line.

For fire.

Section 1. — Works in relation to one another.

136. The distance of works from one another for effective
support by fire is as follows : —

For reciprocal defence by musketry 360 to 500 yards (about a
quarter of a mile, say) between the capitals ; with guns firing
shrapnel, 850 to 1^500 (half a mile to 1 mile^ say) between the
capitals. For defence of the intervals only, these distances may
be doubled.

For the advance of a deployed battalion, regiment of cavalry, or
battery of artillery, 300 yards clear space is sufficient.

For the advance of brigades, the larger interval before mentioned,
850 to 1,500 yards, will be necessary.

On a straight line (Fig. 4, PI. XXXIII.), the capitals of the
works should be perpendicular to the line ; the works, lunettes
with blunt salients, and straight gorges. The works are as it
were the bastions of the line ; and the spaces are the curtains,
either open or closed.

On a convex line the capitals of the works should radiate from
the centre ; the works, lunettes with the salients sharper as the
curve is greater, or blunted lunettes. The gorges t^hould be
broken inwards, to keep their prolongations on adjacent works.
This arrangement is applicable to the defence of a central point
within the line (e.^., bridge heads. See Fig. 1, PL XL 1 1.).

On a concave, line the capitals of the works should converge
to a central point in front. With a very gentle curve, lunettes ;
otherwise, blunted redans. The gorges straight or broken
outwards. This arrangement is applicable to the barring of
defiles. (Fig. 2, PL XLI.)

Intermediate works (a, j^'ig. 1, PL XXXIII.), are necessary
when the distance between the supporting points is unavoidably
greater than the maximum distances before mentioned. They are
usually retired behind the front line not more than a quarter, or
at most half of the distance between the works, to ensure good
fire effect. Their salients, therefore, are not smaller than 120^
(90°, the extreme). They are in most cases redans, or blunted
redans, with open gorges. The profile may be of a light
description. They are good positions for artillery.

187. When the defence is to be a veiy obstinate one, provision
must be made for the penetration of the first line, by adding a
second line of works, forming the rallying position, to l)e at least
600 yards (i.e., out of the effective range of rifles) behind the first
line. It supports the first line with artillery, but necessitates a
fresh infantry attack on the part of the enemy.

The character of the works may be closed redoubts ; the inter
mediate works (if any), open, or half-closed.

F.F.Hatp-XXXlU.

TRACE OF FlELDWURKfl.

o-^

^S:^<?^^-..^^-

■^-^■'

WORKS IN BELATIOX TO OXE ANOTHER. 89

The difltance named gives ample room for the movements of ^or moTement.
brigades.

Advanced works nre frequently necessary to see ground un- AdTanced
seen from the main line, or which may be especially favourable ^^'^'
to the eifects of fire ; or, it may be desired to force the enemy to
develop his attack early.

Advanced works should be within effective rifle range of the main
line ; if possible, under 600 yards. For artillery defence, within
1,500 yards.

The works, of two or more sides according to their prominence. Character,
not being required to make a serious resistance, may be usunlly
open, and need not have front ditches. If necessarily beyond
effective rifle range (an extreme case), they must bo half-closed,
and the work or works then pnrtake of the character of a first
line. (/, Fig. 1 PL XXXIII.)

The tire of the supporting point may be increased if desired by Increasing tin
placing ^^cAe^ on the sides (rf. Fig. 1 PI. XXXII I.) ; these ^;j*"^ ^[.^
are fljuiked by the work and must be well protected by obstacles poi^^*"^
from flank attack.

138. When the ground or condition of the defenders is un- Continuom
favourable for counter attack, the front may be wholly covered '*"^'^*
by defensive works of strong profile*

In this case detached works are designed as before, and the
intervals between them closed by lines of parapet, or obstacles, or
both (Figs. 2, 3, 4, PI. XXXII I.).

The distance of the supporting points asunder, not being Distance of
calculated for movement may be less than before for the sake of pivots,
powerful mutual support by fire.

The connecting lines i^hould be as simple as possible in trace. Nature of
mostly straight, and of as strong a profile as time and means will connecting
allow, but if the intervals to be closed are necessarily great, the ^^"^^'
connecting lines may be traced so as to supplement the flanking
defence of the supporting points. In Fig. 2 the interval is
closed by a couple of bastioned fronts joined together. In
Fig. 3 {a) a central redan gives the additional flanking fire. In
Fig. 3 {h) the line is called indented ; this form is suitable for a
retiring line as it preserves the directness of the fire ; the flanks
must be well protected from enfilade by heightening the parapet
at each shoulder. Fig, 4 shows the intervals closed with obstacles.
In restricted or inaccessible situations with secure flanks, the
enclosed supporting points may sometimes be dispensed with, and
the lines may have any of the forms just described. But
ordinarily the safety of the line, in case of penetration at any point,
is very greatly increased by enclosing portions of it

Narrow openings must be left in the connecting lines for ordi- Entrances
nary communication.

Section 2. — Works in relation to the Ground,

189. The cover for the shooting line, whether mere shelter Cover for
trenches or parapets of strong profile, must be placed generally on 8l»oot«>g ^^'

42642. o

90 APPUED FIELD VOBTIFICATION.

the brow of bills so as to see the forward slopes. Fig. 1, PL XIY .,

illustrates this. The exact position of the crest must be deter-
mined on the spot by the eye. When it is impossible to sweep
the forward slopes all the way without extending the line too fiir
down hill to the front (thus exposing all the grpund behind to
view), advanced lines of parapet or shelter trench must be placed
BO as to sweep the unseen slopes^ such works being treated as out-
works of the main line.

When slopes, unseen by frontal fire, can be swept by flanking

fire at a close range from other parts of the line^ their defence by

frontal fire can Aften be dispensed with^ if it leads to an undue

extension of the works of the main line.

Adaptation to Fig. 1, PI. XIY.^ shows how when the slope to be defended is

their own gites. gentler than J (15^), there is a certain amount of latitude in the

position that can be chosen for the crest. The rearmost position
depends upon the slope of the hill side, the foremost on the greatest
admissible depression for the superior slope (here assumed as :^;
see paragraph 108).

In the case of shelter trenches the variation of position is
extremely small on account of the very small command of their
crests.

Fig. 2y PI. XI V.^ explains the limits for the position of the crest.
The figured contour (30) is supposed to represent the brow of a
nearly level ])lateau. The lines a, b, c, marked by arrow heads
are the desired directions of the fire from the faces of the work on
the summit.

Graduate the line a so as to touch the steepest part of the
surface (in this case the ground between levels 27 and 30). The
graduation is shown on the right-hand side of the line, the depres-
sion being here ^. Having found the point a' (38) (the command
being assumed to be 8 feet)^ this is the rearmost point in the line
at which the interior crest could be placed. If the ground were
not level at top, the levels of the line must be compared with
those of the ground until a difference of 8 feet is apparent.

The lines b and c are similarly treated^ and the points i' and c'
found. The curve drawn through a\ b\ c\ is the rear limit for a
command of 8 feet. For the front limit let the fire from the parapet
with a maximum depression of J, strike the brow 3 feet above the
ground. Graduate the line a from the point dy and for a slope of
J, on the left-hand side. When the level (38) is found, this fixes
the front limit, and the front curved line can be found. The crest
a, i, c, dy may be anywhere between these two curves.

The supporting 140. The supporting points are affected by the irregularity of
points. the ground : —

Their sites, and ]^^—^ \ *® ^^^^,^^ fP"^" ,

distance apart. Ine Sites cnosen should be those from which the best view of

the foreground within range is obtained, or the possession of
which would be most important to the enemy, therefore they are
usually placed on the top of hills and knolls, or on the projecting

Diatance. spurs of plateaux (Fig. 1, PI. XXXIII.). The distance of these

apart will determine whether intermediate wor^ are necessary*

WOBKS IN KELATION TO THE GROUND. 91

The highest point within a position should always be occupied^
and would usually form the key to it.

2nA — As to their form and exact position. Their form and

Their form. — The direction of the flanks having been fixed^ the ?*** position,
faces must be traced so as best to sweep the t^lopes of their own
foreground by musketry.

Their position. — They should occupy the summit of the rising Poeition.
ground, as if on the forward slope the interior would be exposed
to the enemy's fire. The rule about terrepleins, given in para-
graph 109, and illustrated in Figs. 5, 6, 7, PL XIV., especially
applies here.

Half-closed works commanded by other works in rear are well
placed with the interior on tlie reverse slope (Fig. 3, PL XIV.),
as this shelters them more from curved fire, and at the same time
favours their being seen into by the works in rear.

If the works are in second line or in isolated situations, it is
better to place them evenly on the summit with their terrepleins
horizontal (Fig. 4).

It is evident that when the top of a hill, behind the brow, is
extensive, it will not always be possible to sweep the side slopes
from the work on the summit. In this case, as mentioned in the
last paragraph, there must be special works outside for the purpose,
usually shelter trenches ; or the slopes must be seen from flanking
positions.

On ground rising or falling toward the enemy, lines of parapet lines on
must be kept as nearly horizontal as possible, both for cover and ^^^^J^^
freedom of movement of the defenders. towardi the

enemy.

Adaptation to the ground within range. — Defilade,

141. The conditions under which, on irregular ground, the Defilade,
defenders of earthworks are screened from view by the parapets,
together with the manner in which the ground itself assists this
objectj have been already generally alluded to. (Figs. 3, 4, 5, 6, 7,
PL XIV.)

The exact method oF regulating the command of the parapets
of field works when their sites are, or may be, unavoidably com-
manded by the enemy, is called Defilade.

It has been seen that it is out of the question to try and cover
the whole interior of field works from curved fire, and while such
fire lasts, the defenders must shelter themselves by remaining
close behind the parapets or in the blindages. But the interior
of works can at least be hidden from view ; and if this be done,
there is little to be feared from projectiles at close ranges.

Referring to Fig. 1, PI. XXXIV., in order that the enemy on
high ground at £ shall not see the defender at D, the parapet at P
(the position of which is fixed) must have its crest in the line
D E.

For good cover, D should be 8 feet above the ground, and
never le^s than 6^ feet ; E is 4^ feet (about the height of an
ordinary breastwork) above the groimd, and the command of the

Q 2

^gp ngLD FOETinCATION

tnot exceed as a rule 10 feet (in special cases

f***^^ ** ^h^ore explained (para. 109.)

12 fee^)' ^ ^i^Q same amount of cover to be provided at every
S^pP^jl^^crorge iine, the line D E is the elevation (or side view)

point m * 5g plane of vision, called the plane (ff defilade,

^^^ oractice, however, it is not convenient to place the eye at
^'^t V, nor would it be easy to judge of the exact position

fthe point E ; the best plan, therefore, is to place the eye at

^ 3i feet (8— 4 J) above the ground, and observe the top of the

hiJI. In this way a plane called the tangent plane, is obtained,

T^gentp'*"** ^hich is parallel to the plane of defilade, and which fixes the

height of the point p', to which 4^ feet being added, P is obtained

as before.

By reference to the plan (Fig. 2), it will be seen that this
wives the height only at the salient angle ; but if the eye were
placed at any other point/ in the gorge (at the same height of 3^
feet), and the hill e observed from it, this line of vision would
determine the height of the point q in the same manner ; and
thus any points in the crest of the face or flanks could be found.
This is, in fact, the same thing as placing the whole crest of the
work in a plane pissing through the gorge line (+8) and the
point e. The f^ractical method of constructing the tangent
plane is as follows : —
To fiud tangent 1st. For one commanding point as in Figs. 1 and 2 ; let three
plane. upright rods be placed at a, i, c, (Fig. 3), at a distance of about

12 feet from one another; and let a straight edge or cord
(stretched taut), B be fixed at a height of 3^ feet above the
ground. Move the eye along B C until, at a point D, the upright
at a is seen to be in a line with the commanding point e.

The point A, where the line of sight cuts the upright, is marked,
and joined with B and C by straight edges or tightly stretched
cords A B and A C.

Then A B is a triangle in a plane tangent at the points, and
having one line in it B C at a fixed height of 3^ feet above the
ground.

To apply this to the case in Fig. 2. If this arrangement he
set up as at a & c. Fig. 2 with ^ c on the gorge line, the height of
any point in the crest of the faces and flanks can be found by
setting up a rod at that point and marking on it the place at which
it is cut by a visual ray coinciding with the plane of the triangle
ABC. For instance, the point to be marked on a rod set up at
m (Fig. 2), must be in the visual ray c g. To the heights thus
determined, add 4^ feet, and the points thus found are in the crest
and in the plane of defilade,

2nd. When the commanding points within range are two in
number (Fig. 4) ; in this case the work may be defiladed by
placing the crests of its faces in a plane of defilade passing through
a point at the gorge, 8 feet (or 6^ feefc minimum) above the
ground as before, and passing 4^ feet above the two commanding
points, always provided that by this method the conmiand thus
obtained does not exceed the maximum allowable.

nEFJLAUE.

%^^3g

linJ^JiddSIEiafoidS'

F.F.HateXXXy:

DEFILADE.

♦^Vl

\ e

M^-~ ^'

'■^\

Opp to page 33.

^«Ag(!zh.dd..22 Bei£ori S'< Co-nezLt GaxdoL.

WOBKS IN RELATION TO THE GROUND* 93

A practical tangent plane of three points is constructed here
also ; but instead of two points in the triangle being fixed in height
and the third being determined by the single hill, one point. A, is
fixed, and the remiuning two, B and C, are found for the two hills
by placing the eye at A and moving the straight edge or cord
joining the upright rods at B and C until the two commanding
points appear to be on it as at m and n. The fixed point of the
triangle should in this case be at that end of the gorge which
requires the protection of the front parapets from the moit com-
manding point of the two.*

The remaining two rods at B and C of the triangle should be
so placed that both of the commanding points may be seen between
them when the eye is at the fixed point (Fig. 4). The points at
wbich the tangent plane cuts tlie*rods placed at the angles of the
work being marked, 4| feet must be added for the heights of
crest.

AVhen there are more than two commanding points, the two
most commanding points should be selected and the defilading
eifected as just described.

142. When the above methods produce too great a command, Tnyenes and

even with the minimum 6^ feet of cover at the gorge, the work puadot.

must be divided into fportions by large traverses^ or parados,

and each of these portions deBladed separately. Fig« 1,

PI. XXXV., gives a general idea of the method. The distance

between A and B is too great for the parapet at B to give shelter

at A without an excessive command ; by placing a traverse in the

middle at C, the portion of the work between B and C can be

defiladed as in either of the two previous cases (according to the

number of commanding points), the traverse being, as it were, the

gorge of this portion ; and the rear portion between A and C

being similarily defiladed, the traverse being here, as it were, the

front parapet. When there is a gorge parapet (as shown in Fig. 1,

PI. XXXV., it must be screened to 2 feet above its crest, in order

that during an enveloping attack the defenders of the gorge parapet

may not be exposed when standing on the banquette.

Fig. 3 gives what might be the plan of the arrangement shown
in Fig. I,

The position of the traverse or parados must depend on the
shape of the work and the position and number of the commanding
points. For instance, a work at W (Fig. 2), with a projecting
salient, may be exposed to the view of two commanding points
situated as at A and B. In this case, to prevent the faces from
being seen in reverse the parados is best placed along the capital,
stopping short of the salient, in order to allow room for a gun bank.
The portions a e and afoi the faces must be raised by bonnettes
(or traverses on the superior slope) in order to close the open
spaces caused by breaking the length of the traverse.

* The most commanding does not necessarily mean the highest, but that which
has the greatest angle of elevation when viewed from the work, i.e., the relation of
the difference of level between the commanding point and the work, to the distance
of the two asondeTy most be the greatest.

APPLIED FIELD rORTtPlCATIOX.

Here the portions right and left of the traverse are defiladed
independently, in connexion with A and B taken separately, as in
the first case, the fixed line being along the traverse. The height
of the traverse (or traverses) must be regulated so as to protect
the faces and gorges from being seen in reverse by A and B ; the
greater height found by these two independent processes must he
taken.

For instance, for the traverse to protect the portion ah d from
the hill B its crest should be in a plane of defilade passing through
a line h d {S feet above the ground) and 4 J feet above B ; and the
bonnette a^must be in this plane. Similarly for the portion adc
with respect to the hill A. The traverse takes the greater of the
two heights thus found.

In arranging the position of these large defilading traverses,
especial regard must be had to freedom of communication through
all parts of the work. Thus the traverse in Fig. 3 is broken at
the ends to admit of passages round it, the crests of the smaller
traverses being in the same plane of defilade. In a case like that
of Fig. 2, it would be necessary to have blinded passages through
the traverse, kept as low as possible.

These traverses can always be made useful for blindages.
The earth for them should be got from close at hand.

Suitability for
defence.

Defensive
measures.

Clearing fore-
l^ound.

The outer
waUs loop-
holed.

Section 3. — ^Defence of Farms, Villages, and Woods.

Defence of a House,

143. Houses are suitable for defence if solidly built, large enough
to hold at least half a company, and sheltered from artillery fire.
The latter point cannot always be insisted upon ; and provided
that all inflammable substances are removed, and precautions
taken to put out fires kindled by shells, a good defence may stall
be made.

Brick houses, with slate or tile roofs, are the best ; stone
splinters under artillery fire, and wooden houses, or those with
thatched roofs, easily catch fire. A flat roof is an advantage, as
the defenders can fire over the parapet wall through loopholes of
sandbags, &c.

Houses whose parts flank each other, or w-hich have bay windows
or porches, are good.

For security during artillery fire, and before the enemy's in-
fantry arrive within range of the defenders' rifles, the cellars, if
any, will afibrd some accommodation, or splinter proofs may be
built on the principle of that shown in Fig. 3, PI. XXI. The
first wall a shell encounters will generally burst it, and men are
fairly safe behind a second wall as long as some protection is
aflbrded to them against falling splinters.

{a.) The first thing to look to is the clearing of the field of fire,
about which enough has already been said.

{b.) The outer walls should be loopholed, particular xjare being
taken about the flanking arrangements ; two rows should b^ made

F.F.FIat.- mVT.

DEFENCE OF A HOUSE .

DEFENCE OF FAnffl^ yilXAOSS, AND WOODB. 96

on the ground floor if there ii time ; thoee in the upper stories
should slope well downwards in order to see as close to the foot
of the wall as possible. All salient angles should be loopholed.
When the walls are very thick it will generally be easier to form
loopholes under the eaves^ where the walls are likely to be thinner.
With tiled roofs having a high pitch, loopholes can often be very
easily made by removing single tiles just above the eaves. With
flat roofs^ the low parapet walls can be prepared for the use of
men kneeling.

(c.) The ooors and windows on the basement and ground floors
must be strongly barricaded up to a height of 6 ft. by means of
boxes or casks filled with earth or cinder?, &c. &c., or by bullet-
proof timbers secured by baulks and struts. Over the barricades
loopholes can be made in the upper portions of the doors or
window shutters (all glass must be removed), the men standing on
banquettes made out of the furniture. If doors and shutters are
to be made bullet-proof and yet to open, several thicknesses of
planks cut to size can be nailed to them. The windows on the
upper floor need not be barricaded ; blankets, &c., hung across the
lower part wiU screen the men from view, and protection from fire
can be obtained by piling up rolls of carpet, mattresses, sandbags,
&c., to a height of about 6 ft, leaving openings for the men to fire
through.

(d.) To supply flank defence when the building is ill-shaped in Tamboon aad
that particular, tambours may be built out as already described, "^achicoulw.
or *^ machicoulis galleries^^ may be constructed on the upper
floor from which to fire down on the assailants. (Figs. 1, 2,
PL XXXVII.)

(«.) Outside the doors and lower windows ditches should be Obstaclefl to
cut, and the ground around them strewn, with obstacles. dosing.

(/.) To maintain thorough communication between the different Communica-
parts of the defence, passages should be cut in partition walls, tions.
One entrance should be left for communication (on the least en-
posed side of the house) or for retreat- It should be protected
hj a small tambour ; or, if already very well flanked, additional
security may be obtained by constructing a loop holed porch inside
the door.

(y.) If the defence is to be a very obstinate one, the staircases Retrencbmep
should be removed, and loopholes pierced in the upper floors from
which to fire down on the enemy who has gained an entrance.
Communication with the upper floor must be maintained by means
of ladders, ^hich will also serve for effecting a retreat from the
upper windows, should all further defence be hopeless, and a good
opportunity offer.

(A.) To prevent the possibility of a breach, made by the enemy's Precautions
guns in the outer wall, endangering the stability of the upper !!Jf*^°f*.
floor, the latter may be shored up with beams and uprights. ^^^
Materials must also be at hand to barricade any breach that may
be made.

(i.) To provide against fire, all thatched roofs should be re- rrecautiuns
moved ; the floors may be covered with moiet earth or dung, and aga«wt fire.

APPLIED FIlCIiD FOBTIFIOATION.

Defensive
mc*&sures.

there should also be barrels of water and wet blankets in each
room^ a few of the defenders being specially told off as firemen.

PI. XXXVI. and Figs. 1, 2, Plate XXXVIL illustrate the
foregoing remarks.

Defence of a Farm or Group of Buildings.

144. Here the precautioDs are much the sarne^ only on a rather
larger scale. A good distribution of fire must be ensured by
occupying the boundary walls^ taking especial care, as before,
of the flank defence. Small outhouses too inconsiderable for
separate defence should be laid open as far as possible in rear,
and those walls only loopholed which bear on the enemy's advance.
The houses occupied should flank one another and see into all
parts of the boundary, one of them in particular being organized
as a keep ; communication must be kept up as far as possible
between the different houses.

A farm or group of houses capable of holding two or three com-
panies will often form a very good tactical pivot.

Fig. 3, PI. XXXVIL, gives an instance of a fortified farm (Le
Butard). This was one of the posts near Versailles occupied by
the Prussians in the investment of Paris during the war of 1870-71.*

Defence of Villages,

145. The use of villages as supporting points or pivots in a
defensive line has already been referred to in paragraph 113.

4s this kind of defence is wasteful of men, it must always be
decided whether villages would require more men to hold them
than their tactical position may be worth. The number of men
required to hold a similar front of open ground affords a fair test
of this point.

Their principal recommendations are : —

1. That they can be made defensible in the shortest time,

and admit generally of protracted and obstinate
defence.

2. They conceal the numbers and disposition of their garri-

sons and of the troops in rear of them.

3. They afford shelter to their garrisons beforehand.

D'sadvantages. Their disadvantages are : —

1. The scattering of their garrisons and consequent difiSculty

of supervision.

2. Liability of the defenders to loss by splinters, &c., under

artillery fire.

3. Liability to be set on fire by shells.

The object of holding a villnge may be either : —

(a.) as a pivot in the main line ;

(J.) as an advanced poet or outpost ; or,

(c.) as a reserve post.

Use.

Whether to
hold them.

AdTantagei»

Object of
d fence.

♦ See R.E. Professional Papers, vol. 20, p. 8X*

F. F. PkupnXOl.

Fig. I.

Tig.:

%4^isj^

SeaU lOnto 1 inth.

Fig 3

h'l' i' III
'''I ill

//'

\ V

DEFENOB OP FABtfS^ VILLAOBS, AND WOODS. 97

For either of these purposes, the 9aine general rules are applied
to them as to earthworks under similar circumstances, viz. : — If
in the main line (a\ they should be strongly fortified on the
front and flank:>^ and capable also of resisting the attack of infantry
at the gorge, so as to give time for the reserves outside them to
act. If in advance of the main line ns {b), their distance from its
supporting fire will determine whether they are to be obstinately
defended or not, and therefore how much of the circumference
must be fortified. If in rear of the main line (e), an obstinate
defence is sure to be required all round.

The suitability of villages for defence depends upon — Suitability.

1. The form and nature of the surrounding ground, which
should be such as not to include commanding positions within
close range ; to afibrd a clear field of fire with a small amount of
labour ; and, if necessary, to permit of the unimpeded advance,
in the desired direction, of the troops outside the village.

2. The shape of the village and nature of the houses^ <fcc.

The suitability of form to the tactical position affects consider- Form,
ably the time required for preparation as well as the obstinacy of
the defence when prepared. Straggling hamlets lying end-on to
the enemy can be made very strong against flank attacks, but arc
easily mked by fire and require much artificial addition in the
form of shelter-trenche^ &c., thrown out on the flanks, so 'ns to
increase their direct fire ; their length also may be so great as to
weaken the support they may derive from positions in rear of
them, in which case it may be necessaiy to abandon and destroy,
as faivas possible, the more advanced portion of the place, and to
retire the main line of defence towards the centre.

Similarly villages broadside on \ to the enemy are strong in
front and safer from the efiects of fire, but require more attention
on the flanks, and can be less easily retrenched ; whereas those
of a circular form are suitable for all positions.

146. The difficulty of expelling an enemy who has once got into Arrangements
a village makes it especially necessary : — first, to hold the boundary ^®' *^® defence,
obtstinately by a well-extended shooting line with its supports and
small reserves ready to reinforce or expel the enemy ; secondly,
to organize a second line in case of the failure of the first, and
perhaps a keep ; thirdly, to have easy and well-arranged com-
munications to ensure prompt action of the supports and reserves,
and orderly retreat to the interior lines of defence.

The infantry garrison may be reckoned ^t two men (one man Garrison,
the minimum) per pace of the circumference to be defended.

This allows fur reserves. Guns or Gat lings, and engineers
must be added as required; the former dt pending upon the facili-
ties for making use of their long range and for their safe with-
draw^al when capture becomes imminent : the latter depending
upon the amount of skilled labour and demolition by explosives
that may be necessary.

The troops should all be told off by companies and half batta-
lions or battalions, to fortify and defend difl'ercnt [parts of the
village*

avWjIWd field portiwcattok.

Disposition of
troops.
Advance of
the enemy
within range.
Shooting line.
Clearing fore-
ground.

Obstacles.
Coyer.

Gnns.

Supports.

Partial pene-
tration of first
line.

The balk of the garrison (say |- or }) should famish the
shootiog line with its supports^ occupjiog the ciroamference to be
defended.

The foreground must be cleared as usual (see para. 84), and
obstacles plentifully used at weak points. The roads must be
blocked within effective range, and barricaded at their entrance to
the village ; houses flanking the barricades on either side being
prepared for defence.

The shooting line should, as a rule, obtain their cover clear of
the houses^ so as to reduce the losses from artillery fire by back
splinters ; it is considered that a distance of about 40 yards
(minimum) will ensure this. Existing walls, hedges, fee,, will be
utilised as described in para. 104-5. The usual irregularity of
form of such enclosures frequently favours a good flanking defence,
which should always be looked to as a safeguard against the
enemy's attemps to break through the first line ; but the essential
requisite is a powerful frontal fire on the principal lines of attack
Shelter trenches, with obstacles in front if possible, supply the
place of walls, &c., when such do not exist, or do not happen to be
favourably situated. If the front be an extended one, much
flanking power may be obtained by small earthen redans, lunettes,
or sunken caponiers (Fig. 4, PI. XXX.) placed in front of the
first line, and generally so as to close a main thoroughfare. These
works are also of great service in the event of an intended sortie
from the village.

During the artillery fire preceding the attack, and while the
attacking infantry is yet out of eff^ective range of small arms^ it will
be desirable to keep the shooting line well covered ; in trenches
they will be very fairly so, but behind walls it will be often neces-
sary to provide either field-casemates (f)ara. 123) or deep shelter
trenches ; a few sentries left on the front line will watch the
advance.

It is not advisable, though it may be necessary, to place guns
in the shooting line, on account of liability to capture and fre-
quent difficulty of retreat from a much exposed position. Bather
should they be on the flanks, somewhat retired, throwing a cross
fire on the field of attack and commanding the roads (Fig. 1,
PI. XXXVIII.), or on high ground in rear.

A portion of the shooting line must be as usual told off as
supports, their duty being to make good losse?, and to help in
driving out the enemy in case of partial penetration of the first
line. Their numbers need hardly ever exceed half of the front line ;
they must be covered from fire either in the field-casemates or
deep trenches before mentioned ; or behind, or in, buildings close
at hand, when this can be done with safety.*

To provide additionally against the partial penetration of the
first line by small bodies of the enemy, short lengths of wall,

* Troops in an ordinary house are not safe under artillery fire, unless in cellare
or field casemates. Behind a house they would not suffer mnchj as the sheUs would
be usually exploded by their penetration of the outer wall.

\^ I ^^^^,a

DEFENCE OF PABMS, VILLAOES, AND WOODS. 99

hedge, &c. which may run perpendicularly to the shooting line and
within it, should be prepared for defence, in order to prevent the
assailants who may have forced their way in from ppreading along
the line. This arrangement also favours the division of the place
into defensive sections.

147. In case of the failure of the first line, there may be a second Failare of
(and even a third) line of defertco, manned at its principal salients *"* ^^^'
by troops from the reserve ; behind this line the beaten troops ^"»w of

retire by well-defined routes, forming again either to aid in its '**"'»<^^™«o**

defence, or as a reserve.

The cover for this line or lines will usually consist of an Coyer,
irregular line of loopholed walls and houses made as impenetrable
as possible ; where roads cross the line they should be barricaded.
Here the fighting will be of a close nature, and a close fianking
fire is especially valuable. Houses immediately in front of this
line should be cleared away or gutted to prevent the enemy from
closing in order to make breaches by means of explosives or other-
wise. Small bodies may be held in readiness to charge the
enemy in case of penetration, as with the first line ; and a few of
the houses at favourable fianking situations may be loopholed and
barricaded all round to act as section keeps.

148. When a village is intended to be held to the last, though Keep,
surrounded by the enemy, a substantial building or group of build-
ings and enclosures may be prepared for defence as a keep to the
whole. Here a resolute- few must hold out till assistance arrives.

It is evidently useless to prepare a keep if such desperate resist-
ance is not intended. The real object of the keep is to facilitate
recapture by having one foot, as it were, in the place ; and as its
garrison cannot be large, and must be (unlike the retrench-
ments) kept separate from the rest, it could not obtain this result
unaided.

Buildings with thick walls, and having a good form for flank Nature of keep,
defence, are the best. They should be well out of view of the
enemy and if possible sheltered by neighbouring houses, &c. from
distant artillery fire. Close artillery fire is hardly to be feared, as
the constant fire of rifles from the loopholes of the keep would
make the service of a gun almost impossible. Churches and large
storehouses would generally answer as well as keeps.

149. The communications are of the utmost importance ; they Comnmnica-
should provide the means of moving easily all along the front of ^^^^*

the various defensive sections ; and also in a radial direction for the
rapid advance of supports and reserve?. Finger posts must be
freely used to direct, and if necessary orderlies must be posted at
important points for the same purpose. No communication should
pass through the keep.

A few of the garrison should be told off to take the best Precautions
measures for extinguishing all fires, having water ready at hand. agaiDst fire.

If possible, not less than a company (or at very least a half Defensive
company or subaltern's command,) should be told off* to any sections.
defensive section. The keep would require from one company to
a half battalion.

100

APPLIED FIELD FORTIiriCATION,

Gatlings.

Goard-houses.

Hospital.

Order of
importance of
(lefensive
i rrangements.

Village of
ChcTilly.

Oatlingd would be very usefully placed behind barricades, to
sweep long broad streets. Care must be taken that they are not
exposed to the enenoy^s artillery during the early part of the fight.

Some of the houses should be used as guard-houses to furnish
the ordinary guards.

A bombproof building in a sheltered situation should be fitted
up, or purposely constructed for the accommodation of the sick
and wounded.

150. The arrangements for the defence, in order of relative
importance, are, —

1. Clearing field of fire.

2. Covering shooting line, supports, and guns.

3. Placing obstacles.

(Part of this would generally go hand-in-hand with (1).)

4. Making communications.

5. Constructing retrenchments and keeps.

The salients of the first line of defence are its most important
parts ; next the flanking and re-entering portions. After this the
closing of all gaps by obstacles, as well as the placing of obstacles
in the foreground.

With an adequate garrison a period of about L2 to 18 hours
would generally suffice to fortify a. village strongly.

The figures in Plates XXXVIII. and XXXI X:. illustrate the
foregoing remarks. Fig. 2., PL XXXIX., shows tlie distribution
of troops for the defence. This village was actually the scene of
a combat in the war of 1870-7 1, when it was held by the Germans
against a sortie of the French from Paris. The defenders were
posted much as here shown, but sufficient care had not been taken
in occupying the farm at b and blocking the hollow roads near it;
a wall at a had also been left standing. For these reasons the
French managed to take the farm, and though ihey pushed their
attack no further, its recapture cost many lives, and was mainly
brought about by the failure of the sortie in every other direction.

Woods.

151. The fortification of woods is similar in principle and general
arrangement to that of villages. They are very effective in
screening the defenders from view, and give more or less cover
according to the size and closeness of the trees ; this very closenes.^,
however, is a hindrance to the united action of the defenders, and
makes it extremely difficult to expel an enemy who has once
gained a footing in the wood. Moreover, the construction of lines
of retrenchment for further resistance is a work of more time and
difficulty than is the case with villages. Therefore the main object
of the defence is to hold the edge of the wood very strongly, and
to take special steps to ensure the prompt action of supports and
reserves in case of the boundary being forced at any point.

Well-timed flank attacks by the reserves (however small) are
of great service in repelling an enemy who is trying to force his
Way through*

f . F. 1'1;H.- XXXK

F. F. PW» XL.

DEFENCE OF FABMS^ VILLAORF9 AND WOODf* 101

The same garrison may be oflsumed as for villages, viz., one to GhniMiu
two men per pace of curcumference defended. They should be told
off to different sections in tactical units, the bulk of the men being
in the shooting line.

Whether the shooting line should oocupy the whole edge br Shooting Uncb
only portions, must depend upon the size of the wood and the
difficulties of approach ; but in any case it is advisable to provide
iin obsticle all along the boundary, if possible, by felling the trees Obntaclc,
to form a rough abatis a dozen or more yards wide. Large trees
should be left alone ; they give cover to two or three men, nnd
require skilful woodmen to cut them down. The most important
parts of the boundary are the salients first, and then the re-
entering angles ; the former are, as it were, the bastion?, and the
latter being most retired provide flanking fire to the former, for
as long a time as possible. Should time press, tiiesc are the
portions to look to. There should as usual be obstacles in the
foreground, to increase the effects of fire without screening
iix>m it.

The shooting line obtains cover behind the abatis in trenches. Cover for
or by adapting hedges and ditches, where such exist, as explained *^ooting line,
in para. 104..

The supports and reserves are safe if so far in that they cannot Supports and
see the open between the trunks of the trees ; otherwise, or if the '*"«'^"-
timber is not sufficiently close or well grown to resist rifle bullets,
they must be covered liy trenches.

Entrances of roads must be barricaded witli felled trees, or if
communication is to be preserved the barricade must he in •
advance of the general line of obstacle, leaving passages on either
side, or an earthen redan or lunette may cover the entrance.
(PI. XL.)

If a wood is supported by the artillery from other parfsof a line Gans.
guns should never be placed in it. Tiicy are better outside on the
flanks, as in the case of villages ; if unavoidably placed in a wood
on the boundary, they should be spaced at wide intervals and near
good roads, either existing or made on purpose, by which to
retire. They should be concealed from the enemy, and each gun
should have two or more places from which it can be fired at
pleasure.

152. To localise the combat after penetration of the boundary Retrench-
at any point, lines of abatis should be made perpendicular to the ™«^*8«
boundary, and extending from 50 yards to 100 yards inwards; Short radial,
these radial retrenchments may with advantage correspond with
the tactical divisions of the defenders.

Any open spaces, brooks, or broad roads running through the Second line,
wood in a direction parallel to the front, may be taken advanta<ye
of to form a second line, secured against a rush in the same way
as the first line, by abatis, and other obstacles on the front and
flanks, leaving as much clear space in front as possible, for fire
effect. A good sized building or enclosure would form a keep.

Communications are of the utmost importance, and the roads Communica-
and paths selected or made for the supports, reserves, and guns ^'®°**

102 ^ APPLlEJp FIELD FOBTIFICATION,

miigt l>e well defined by hlaziJig the trees with an axe, and by
leaving sentries in addition at crossings to give directions.

In dense woods preparations should be made for blocking the

roads in case of retreat, by cutting trees on either side nearly

, through, in readiness to be pulled down across them, leaving the

upper part still hanging to the trunk to prevent their being easily

pulled aside.

Besides these radial communications, there must be the means
of moving freely along the boundary.

Special Positions in or near Woods,

In middle. 153. If a position must be taken up in the midst of a wood, ft

is treated in the same way as a retrenchment.

On rear If the rear boundary is to be held, the same rule applies, care

boundary. being taken to leave a narrow belt of trees behind the clearing to

screen the defenders.

Behind a wood. When the occupation of a wood would lead to too great exten-
sion, a fortified position should be taken up about 600 yards (the
effective range of rifles) in rear of it, the trees on the near border
felled to form an abatis, as an obstacle to egress, £»nd tlie roads
strongly barricaded.

A heavy fire of guns and rifles should be directed on all the
most probable points of egress.

Fire. Should the enemy succeed in setting a wood on fire to any

considerable extent, it must be evacuated and the position behind
the wood taken up as quickly as possible.

These remarks apply also in principle to positions in rear of
villages.

Section 4. — Choice op Defensive Positions.*

154. In the last chapter, under the heading of " Trace of Field
Works," the entire subserviency of field fortifications to the
tactical objects of the fight was alluded to. It was seen that the
benefits it confers consist not only in giving cover in general to
all troops engaged, but also in the provision oi pivots or supporting
points to the defence. The full advantages of fortification can
only be reaped when there is ample time for preparation ; but the
shortest time that may be available will allow of the construction
of works sufficiently formidable to produce a great economy of
force on the defensive, and to enable more force to be thrown
into the counter-attack.

The tactical situations which may arise must now be treated of
in greater detail, and the particular bearing of fortifi.cation on
those cases pointed out.

Tactical Objects of the Defensive,

155. A position may be defended with one of two main objects.

VIZ.

* For full information on tactics, the reader is referred to Home's " Precis of
Modem Tactics,'* Sir G. Wolsele/a ** Soldier's Pocket Book," &c.

CHOIOE OF DBFBNSIVE POSITIONS, 108

(a.) With a vievr to Bhattering the enemy by fire before OffeDBive
assuming the offensive^ at the critical moment^ a line of action ^^<™*>^«*
usually termed the offensive defensive,

(&.) To hold one's own ground, either with the view of denying The pure
its possedsion altogether to the enemy^ or of keeping him at bay ^^^^^*^e-
for a while.

The former case is chiefly applicable to battle-fields when a Application of
force equals or not much inferior, to its opponent has found a J^'"*.^©
good position, barring or threatening the enemy's line of advance, ®°**^^-
and at the same time so favourable for defence by small numbers
that a large proportion of the force can be kept in hand for the
final attack.

As the essence of this mode of action consists in the attack
beino: induced in the right direction, the enemy is usually not far
distant, and the time for preparation is in consequence limited to
perhaps 24 hours or less. An elaborate preparation for the
defence of such a position would be ill repaid by the discovery
that the enemy had marched round the flank and so turned the
line.

In 1815 the Duke of Wellington, wishing to ^ve battle on the
field of Waterloo, abstained from entrenching bis position, lest be
sbould deter the enemy from attacking bim.

The pure defensive can only be adopted definitively when the Application of
flanks are secure. The various cases of this which present them- pure defensive.
selves are as follows : —

Defence of a complete circle &om within — ^intrenched camps,
dep6ts, double or manoeuvring bridge-heads^ environs of an
invested fortress.
Defence of a complete circle from without — alines of investment.
Defence of a portion of a circle from within — ^protection of
communications over natural obstacles^ such as rivers, moun-
tain ranges^ &c.^ to secure operations on the further side.
Defence of a portion of a circle from without — denying the

pas^sage of the same obstacles to the enemy.
It may, however, be adopted temporarily, as by a rear-guard,
to delay the enemy's advance, in position^ that can be turned.

Formations of Attack and Defence.

156. As the defenders must be disposed in that order of battle
which will best meet the method of attack adopted, a short
descriptii)n of the latter is here given. A detailed account of the
mode t»f advance practised in the British service will be found in
the '' Field Exercise."

The accuracy, range, and great rapidity of fire of breech-loading Tactics of
rifles have caused the older more serried order of advance, so attack.
favourable to perfect control over the troops, to give way to a
looser method, demanding much more individual self-reliance.
The increased difficulty of control over men once launched into
action, as well as of keeping them supplied with ammunition,
makes it important to retain the close order until the severity of
the enemy's fire actually forces an extension, and when once that

104

• APPLIED FIELD POBTIPICATION.

Phases of
attack.

Method of
advance.

extension lins occnrred each tactical unit Bliould be advancing
with A definite object in view, as changes of direction or purpose
cannot without great difficulty be afterwards effected.

157. A frontal attack by a mixed force may be considered as
consisting of the following pliases, bearing in mind that the«e may
merge into one another in praclice, so that it may not be easy to
see where each begins and ends : —

1. Preparation for the infantry advance by means of a powerful
concentric fire of artillery, in order to shake and paralyse
the defender and to destroy material obstacles.

2. Preparation for the assault by means of the infantry advance,
attempting by fire to overcome the defenders* power of
resistance.

3. The advance to the assault of the same infantry backed up
by the reserves.

The advance under fire is conducted by a line in extended
order, the extension taking place at effective artillery range, say

Attacking line. 3,000 to 4,000 yards in the open. Within the range of aimed

musketry fire (say 800 yards) ground is gained by the alternate
rushes of companies over distances of 30 or 40 yards. They take
advantage of any cover tliat offers itself in their line of advance,
to lialt and deliver a controlled and deliberate fire.

Supports. This extended attacking line is followed up from the commence-

ment by a line of supports of about equal strength, who make
good losses and reinforce when necessary, and are therefore as
close up as they can be without sharing the losses of the first line.
A distance of about 300 yards to begin with will suffice, which i^
gradually reduced as the advance proceeds, until when the attack-
ing line arrives at close range (100 to 300 yards), the two lines
intermingle and pour in a rapid independent fire. This period is
usually considered the crisis of the atteck, which now only
requires a charge at a favourable moment for its completion.

Reserves. If a real attack is intended, the advance described above must

be usually backed up by a reserve line about equal in strength
to the attacking troop:». They might be at commencement about
500 yards behind the supporting line, and would gradually
diminish this distance during the lialts and checks of the latter,
until, when the charge is given, they will be following close behind,
and doubling the weight of, the charging line. On fresh troops
would devolve the duty of pushing the success further, if needed,
the exhausted troops of the attack being collected and formed in

reserve.

Thus, whereas, until lately, skirmishers by their fire covered
the advance of the masses that made the charge ; now the
skirmishers make the charge, being constantly fed by troops in

rear.

Supporting
lines.

Independent of the troops making the assault, there may
be, as occasion demands, other lines in rear to protect the advance
from counterstrokes, and to fill up gaps«

CHOICE OP DEFEKdlYE POSITIONS. 105

1.58* The artillery woulil come into action at about 3,000 yards ArtlUeiy of the
^ess, if possible), in the open ; besides preparing the way for the ^^^^^'
infantry attack, it endeavours to support them in every way by
drawing the enemy's fire on to itself, using at the same time every
ncciJent of ground^ &c. which can give it cover. Its final posi-
tion might probably be 1,000 to 1,500 yards from the enemy's
main line. It is generally unadvisable for artillery to approach
uncovered within 1,000 yards of infantry.

The aid contributed by cavalry in the attack is very limited as Cavalry,
a rule^ on account of the exposure which its movements in the
open entail. Bat if small bodies of cavalry can be pushed for-
ward towards the flanks unobserved, and kept covered from the
enemy's fire, they will be of great value in giving warning of
or checking flank attacks made by the defenders.

159. The advantage of the attack, apart from the general supe- Offensive and
Tioiity of numbers, and the benefits which accrue from this in defensive
power of outflanking and repetition of effort, lies chiefly in the ™2 ^™"
assumption of the initiative, leading to concentration of strength

towards the object in view ; and although the defender by the
possession of a good strategical position can sometimes attract the
assailant, and lure him into an attack in a certain predetermined
direction, yet defensive action has, as a rule, the disadvantage of a
certain amount of suspense as to the enemy's main object, with the
accompanying uncertainty as to where the bulk of the reserves
shall be massed. Any other advantages of the attack are chiefly
of a moral nature, such as the excitement of forward movement,
and the ignorance while moving of the extent of the losses that
are being incurred.

160. The defensive measures adopted to meet such a mode of
Attack as that just described are of a similar general character.

The enemy's preliminary cannona:le is met by the defenders'
guns, which will endeavour to force an early deployment.

In this they- may be assisted by small bodies of infantry and
cavalry, especially the former, who will endeavour to keep the
enemy's infantry out of rifle shot of the guns ; by such means
time is gained for bringing up reserves, &c.

To oppose the infantry advance, the main line of the defenders' Infantry
infantry should be extended so as to sweep the entire foreground dispositions,
within effective range of their rifles, and especially at ranges
between 200 and 400 yards. But instead of a straight and per-
fectly continuous line, the variations of the ground will almost
always dictate a line alternately £>alient and re-entering, and the
troops will be chiefly gathered together at the more salient por-
tions whence the best view is usually obtained.

Such points the defenders under cover should hold by their
fire, for the proper production of which they are elxtended so
that each man may occupy about one pace of froiit (this admits
of the maximum fire-effect). Tliis first line has, as in the atttack,
its supports, which may be of about half its strength, as the Supports.
losses in the defence, are not likely to be so great as in the attack ;
accidents of the ground, too, will generally allow of their being

42642. TT

106

APPLIED FIELD 70BTIFI0ATI0N.

Third stage of
the attack.

Counter-
attack.

Manner of
delivery.

kept close up to the first line^ so that no time need be lost in

replacing casualties.
Local resenrefl. Behind the supports are the immediate reserves^ which may

be about one-half the strength of the remainder. Thus^ a three-
battalion brigade might haye two battalions in front line and one in
reserve. Each of the two in front line might have (with eight
companies each) fiye companies extended and three in support ;
or six extended and two in support, if they were very well
covered.

It is not here intended to lay down any rule as to the telling
off of the troops into the various bodies, but merely to give a
general idea of the arrangements. In our service the half-
battalion is generally the tactical unit.

When the attacking line is delivering its final rapid indepen-
dent fire previous to the assault, the defenders' supports will have
reinforced the first line, and the enemy must be met in his own
fashion. When the fire of the defenders has told to the utmost
upon the assailants and checked them in their final charge, a
favourable moment generally arrives for counter-attack.

The extent of the latter, whether on a large or small scale,
must depend on the circumstances of each case, but the defenders
must be very weak, and in a very restricted situation, if they are
unable to make use of so powerful an auxiliary to the defence.

It is ^nerally considered that the counter-attack should not be
delivered by the troops who formed the shooting line, but by tlie
reserves, either local or general ; and as the essence of the counter-
stroke consists in its rapidity and force, the troops that are to
make it should be close at hand (sheltered by groimd, or artifi-
cially) and already in a suitable order of attack. Necessarily, also,
their attack must be unimpeded by the ground or by any defensive
arrangements.

Small attacks straight to the front are generally made by the
local reserves, but attacks on a larger scale (in the assumption of
the offensive) should be made by the general reserves, and are a»
a rule most effective when circumstances permit of their being
made from a fiank, for then they do not mask the fire of the troop&
in the shooting line, and have also a greater moral effect

The extent to which coimter-attack is to be used is the great
point to be kept in view in selecting fighting ^ound, and has, as
already seen in the previous chapter, everythmg to do with the
arrangement of fortifications. In some cases (the offensive defen-
sive) the counter-stroke is the grand final object on which the whole
defence turns ; in other cases (the pure defensive) it is only used
as a means towards a more effectual resistance.

161. The defenders' artillery should be able to concentrate their
fire on known lines of approach. During the advance of the
enemy's infantry it should aim at that arm which threatens most^
and on which it can produce the greatest effect ; this will usually
be on the more compact bodies of the supports and reserves.
During the crisis of the attack, flanking portions of the guns are

B61eofthe
defenders'
artillery in
final stages.

CHOICE OF DEFBNSIYE POSITIONR 107

especially desirable^ or poaitioDB on higher ground in rear^ out of
close range of the enemy's rifles^ ana yet such as to allow the
artillery to be e£S^tive till the last moment.

In using the flanking fire of guos the dispersion of the frag-
ments of their projectiles must always be remembered. The cone
of dispersion of case is often as much as 100 up to 200 yards
from the gun. The dispersion of shrapnel is about 6^ or 7^ from
the burst, and the splinters of common shells range 400 or 600
yards.

162. When a position is to be obstinately held, a second line Second line,
may be posted in rear^ behind which the first line may retire^ and

upon which the enemy will have to direct a fresh attack.

A post may be held in advance of the main line, either on Adyanced
account of its importance in seeing ground unseen firom the main ^J?!Jlf^
line, or because its possession would be of great advantage to the **"^^^'*^"*
enemy as a basis of attack.

The manner in which it is held depends greatly on its distance
from the main line. If the latter can support it effectually by its
fire it is a source of strength to the defence, as the enemy cannot
pass it without being taken in flank ; but if beyond the efiective
range of the main line, an outpost position cannot as a rule be
obstinately held without absorbing too great a force in its defence,
and its principal use would be the infliction of some loss on the
enemy, whilst forcing him to deploy early and develop his plan of
attack.

Influence of Ground,

163. The ground, both as to its main features and the accidents of
its surface, has obviously so much to do with the development of
fire and facility of movement of troops, that it becomes a very
important factor in all defensive questions.

Looking to the main object of the fight, the value of the ground As to object
depends on the extent to which it favours that object. If a pure ®^^8^*-
defence is intended then the ground is good in as far as it presents ^^^^ defensive,
difficulties to the advance of the assailant, and narrows and breaks
up his front, e.ff.y a position behind an unfordable river or other
natural obstacle, or behind rugged and difficult scarps, and so on.
These characteristics are especially desirable on the flanks, as in
any case of the pure defensive the power of overlapping the
defenders in point of numbers must generally be conceded to the
assailants.

For the offensive defensive the ground should conceal by its folds Ofiensive
and accidents the positions where the reserves are massed, and ^^^^^^^e.
allow of their unimpeded advance in the desired direction, whether
to the front or to a flank ; it t»hould not by its formation to the
front aid the assailant in taking the defensive when pursued.

Although there may be and are cases in which the ground
would be suited wholly to either one or other of these two classes
of actioni yet it most ofteu happens, when the front is at all

H 2

108 APPLIED FIELD FORTIFICATION.

extensive^ that the nature of the ground dictates a corresponding
division of it into offensiye and defensive portions, and the com-
mander must make his detailed dispositions accordingly. When
the country is much enclosed and wanting in relief it is not so
well suited to prompt action with a large front, and the defence
must be deeper in arrangement, providing successive lines to fall
back upon; whilst with an open country, permitting of free
movement with a large front, and powerful fire effect, so great
defensive depth is not required. In the latter case the reserves
must be close at hand.

The ground 164. In considering the influence of the ground on the actual

with reference gght, it has to fulfil the general principles of defence, viz. : —

defence. (^ ) Exposure of the enemy.

(6.) Cover of the defenders.
(c.) Obstacle to the enemy.
(d.) Freedom of movement to the defenders.

For exposure -(^O ^^ order that the enemy shall be exposed to fire at all
of enemy. ranges, especially within 600 yards, the surface should be firee

from obstructions; and the features of the ground itself will
provide less cover to him when the country is generally undu-
lating rather than having deep valleys with steep hillsides.
Infantry shoot- The most favourable position for commanding a view of the
ing position, slopes is the forward brow of a hillside, and here consequently

the shooting line is plnced, the salient portions being the most im-
portant as they first receive the enemy and take him in flank if
he passes them. These positions should be arranged for the purely
defensive, and any natural strength they may possess increased by
artifice. This may be the more freely done as counter-attacb
should proceed from the re-entering portions between the salient;
the latter are the decisive paints of a line, and must be tena-
ciously held. In considering later the application of fortification,
their value will be more prominently brought out.

Cover of (p-) Cover of defenders has been fully dealt with in detail in

defenders. the elementary chapter ; the power of sheltering and concealing

the reserves by the formation or circumstances of the ground
must be specially looked to. For this, steep reverse slopes are
desirable, subject to the necessity for freedom and rapidity of
movement. The massing of reserves unseen oflTers obvious advan-
tages to their tactical action.

-Obstacle to the (s-) Obstacle to the enemy may be provided either by the relief
enemy. of the surface of the natural ground, or by the nature of that

surface.

The following table, extracted from "The Soldier's Pocket
Book," by Sir G. Wolseley, explains how the slopes of the ground
affect the movements of troops. A slope of 5° (about ■^)t^}^
extend for a few hundred paces, is a severe check to a rapid
advance ; and on slopes of lO"* (|) and upwards a rush for anj
distance is ioapossible.

CHOICE OF DEFENSIVE POSITIONS.

109

Gradients admitting of Manocnvrea.

Infantry,

May move irith order,
ftDd has down hill the
most effectual fire and
charge.

Cavairy,

May moTe with order
and charge effectively
either up or down hill.

Artiliery,

Has a more effectual
fire down than up hilL

Infantry,

Its close movements
become difficult •

Cavalry.

Can only canter down
hill ; chaiy^e only pos-
sible up hill.

Artiliery.

Moves with difficulty;
its effectual and con-
stant fire ceases.

«;'

Infantry,

Cannot move &r in
order; fire up hiU in-
effective.

Cavalry.

May still trot up and
walk down hill.

Artiliery.

Moves with great diffi-
culty ; fire ceases.

Gradients that may be ascended and descended singly.

20°

25**

SO''

Infantry.

Light Infantry.

Infantry.

Cannot move in order,
and can only fire
singly with effect

As for 20*^.

As before.

Cavalry.

Light Cavalry.

May ascend at a walk,
and descend without
order, and that only
obliquely.

. , *-

May ascend one by one
obliquely and descend
in the same way, but
with much difficulty.

M^y ascend obliquely,
but with great diffi-
culty, and when the
slope is of soft earth.

As to the nature of the surface^ account must always be taken
o£ the softness or roughness of the ground, as especially affecting
rapid rushes. A ploughed field in moderately wet weather^ for
instance, is a considerable impediment to an effective charge.

(i) Freedom of movement for the defenders is equally affected Freedom of

by the above table. dS^T^' ^^^

Freedom of movement is always required within a position ; in
advance of the line it depends on the necessity for counter-attack.

165, The ground also affects the positions for artillery. Artillery pom-

From eminences the distant foreground can be best seen, and
from salient and flanking positions the near foreground can be fi^^ ^^^ "*
best swept by fire.

Our 16-pr. field gun carriages admit of a depression of 12 J° ; if
the slopes of the ground, therefore, are steeper than this, the
artillery fire does not take effect except at long ranges, or
obliquely.

For protection from fire, a brow at the top of a reverse slope is For protection
a favourable position, as the gun itself need only be so far forward ^^ ^^'

110

APPLIED FIELD FORTIFICATION.

Protection
from assault.

For facility of
movement.

Positions on
high ground in
general.

The decisive
points of
heights.

as just to clear its line of sight, and the limbers and teams on the
reverse slope are screened by the brow {see Fig. 7, PI. XII.).

Hard, rocky, or stony ground increases the effect of splinters,
but soft ground close in front of the guns catches many and
reduces loss.

Eocky scarps or other obstacles in front of the suns are of
advantage in protecting them from capture, especially in front
line, provided, of course, the obstacle does not interfere with their
movement. The less, however, the guns need be moved the
better.

Where movement is necessary, the ground should be hard and
smooth. The table just given treats of the practicability of various
slopes.

166. The possession of high ground offers many advantages to
a defensive force, not only exposing the enemy's movements, but
concealing those of the defender, and providing natural cover and
obstacles.

The decisive points of heights are the higher summits, as the
possession of these would give the enemy the advantage of
command now enjoyed by the defender.

Along a
plateau.

Forward hrow.

On rearward
brow.

Positions on Heights.

167. Positions on heights may be classified as follows : —

(a.) On a plateau.

(^.) On a hog's back or narrow ridge.

(c.) On the lower spurs of heights.

(a.) On a plateau.

Here either the forward or rearward brow may be occupied by
the main shooting line.

The forward brow is the most favourable position, as com-
manding a view over the whole of the ground in front. Advanced
terraces and knolls on the forward slope can be occupied by guns
and infantry told off to begin the fight.

The salient spurs are the best infantry positions for the shooting
line, for reasons before stated, and when the plateau is level they
are the decisive points. When the top of the plateau is undu-
lating, the summits next to the brow are the decisive points. If
other summits again occur behind these, they form the important
points of the reserve position. Some of the guns may be well
placed in the re-entering bends of the forward brow, from which
positions they will flank the salient spurs. If retired far behind
the brow, their effect on the forward slope would usually be
much diminished.

If the forward slope is too much covered by obstructions to fire,
or too steep for proper fire effect, a position may be taken up
along the rearward brow, using the summit of the plateau as the
foreground, if it is suflSciently wide and clear. In this case the
main position should be well in front of the rearward brow (500
or 600 yards), so that the latter may be used for the reserve

CHOICE OF DEFENSIVE POSITIONS. Ill

positioi]. The latter position is important, as in the case of
retreat the troops would otherwise suffer much from the fire of
the enemy who had gained the rearward brow, and the more
so in proportion as the reverse slopes were bare and difficult of
movement.

The decisive points here arc the summits next to the rearward
brow.

168. If a position fall across a plateau the same rules hold good. Actom a
Here the object would generally be to extend the limited line ?>•*««•
by taking up positions on the lateral spurs, preventing the turn-
ing of the line and bringing a cross fire to bear on the central

part of the position. In extensive positions the line may have to
be ; rolongea down into the valleys ; in which case it is well for
the lower part of the line to be somewhat retired behind the
higher, so as to receive the flanking artillery fire of the latter.
Knolls and terraces on the slopes should be taken advantage of
for flanking batteries.

(^.) On a Hog*s Back or Narrow Ridge.

169. A position along the ridge is not very desirable for an Along a ridge,
active defence^ as although it offers great facilities for covering

the reserves, Jhe latter are restricted in manoeuvring power.
For more passive defence the position is more favourable^ but
even here the want of depth would be felt^ as it could not be easy
to find a good position for a second line of defence. The more
commanding summits of the ridge are here of great importance^
as they are not only the keys to the first line, but if taken are
favourable points for the enemy's artillery to occupy while plying
the retreating defenders. These disadv^tntages are only lessened
when the reverse slope is very gentle and well covered with
natural objects, &c.^ when the case becomes almost similar to
that of a plateau.

170. Sometimes a line would have to cross a narrow ridge ; this Across a ridge.
ia a restricted case of a line across a plateau. The summit of the

ridge should be under a heavy fire, and the defence at this point
of a passive nature, obstructions being plentifully placed in the
enemy's way.

171. Generally undulating ground, which forms neither distinct Undulating
plateau Hor ridges, may be broadly regarded as embracing modi* ground,
fied cases of both in different parts of the battle-field, and posi-
tions on this kind of ground follow the same general rules.

(c.) On the Lower Spurs of Heights,

172. It sometimes occurs that the forward slopes of plateaux or
mountain ranges are of such length and extent that a position on
the summit is not desirable. In this case knolls and spurs are
generally found to form decisive points and pivots, and the case
is like that of undulating ground. The position is so far un-
favourable that the retreat must be conducted generally up hill in
view of the enemy, but the summit affords a good reserve position,
and beyond this point the retreating troops are well protected.

112 APPLIED FIELD FORTIFICATION.

A very gentle forward elope is to all intents and purposes a
plateau^ and can be treated accordingly.

Main points of 173. In general the Lighest summits within range are the points
irregular of greatest importance or decisive points^ the possession of which

groun . must be forbidden to the enemy ; and those brows which com-

mand the best view of the ground in front mark the positions for
the main shooting line.

Qualifications 174. To recapitulate, then, the qualifications of a defensive
of a position, position in accordance with the general principles of the defence

are :

1. Suitability to the strategical and tactical objects of the fight^
as before explained^ especially with regard to counter-
attack.

1. A clear field of fire, especially at the most effective ranges.

3. Cover for the troops in action and for the reserves.

4. Free communication within the position, both lateral and to
the rear, with room for the reserves, and secure lines of retreat.

6. Facility for making obstacles at defensively-held portions
of the line.

Section 5. — ^Fortification of Positions.

Application of Works.

Halation of 175. It is usual, in estimating the force required to hold a

forces to front, certain position, to reckon it at so many men per pace of front

occupied.

In the open the number might be five to ten men per pace^

according to natural strength of ground ; with fortifications, three

to six.

Points to The points to fortify by cover and obstacle, as rtrongly as

fortify. ^jp^g ^yjjj allow, are the supporting points, or pivots, from which,.

as before stated, no advance is to be made, and which will there-
fore admit of it. The normal arrangement of these as regards
their effective support of one another and the intervals required
for movement, has been treated of in Section 1. The decisive
points of heights as well as defensible localities (farms, villages,
woods), are points from which a selection would be made.

These are the safeguards of a line during the close ^attack ;.
their fire should be sufficiently powerful (i.e., the fire-lire sufiSn
ciently extended) to attract the assailant to attack them ; other-
wise they could be surrounded and masked by comparatively
small numbers while the intervals were forced. The clo««er they
are to one another and the more fire they .furnish (depending
mostly on their accidental size in the case of localities, and on
the resources for their execution in the case of earthen redoubts},
the greater will be the defensive strength of the line, but the
less its offensive strength, on account of the greater numbers
absorbed in passive defence. Their distance and nature must be
therefore determined by considerations of tactics and of the
groufidf - * - . - -

FORTIFICATION OF POSITIONS. 113

The garrisons of the supporting points may vary from one
sixth to one third of the whole defensive force> exclusive of
troops held in hand for the offensive on a large scale, leaving
five sixths to two thirds of the force for defence of the intervals^
according to circumstances.

The action of the supporting ])oints or pivots must not be
confused with that of the shooting line^ though in eome cases
they may coincide.

A thorough sweeping of the front with fire being the first

object, the men must be extended along brows of hills, &c.,

wherever the best view can be obtained, covered by shelter

trenches or natural objects. This provides the necessary amount

of infantry fire under which the enemy has to effect his advance.

Their positions should be strengthened by obstacles, except when

t\\ey happen to be on a line reserved for counter-attack, in which

case the ground must be clear, and the cover consist of nothing

less easily passed than a shelter trench. Further, the security of

the line from capture is ensured by the fortified pivots, assisted

by the troops outside them. Their special duty commences

therefore later, when the enemy is already almost amongst the

defenders.

The respective merits of field-works and fortified localities
have been already discussed elsewhere {see par. 113).

176. The fortification of the artillery positions consists almost fortification*
entirely in making gun-pits and epaulments, for use at all stages ^^^'^'

of the fight. Some, therefore, are pushed out to the front (when
the retreat of the guns is easy) ; others, intended for the defence
of the main line, are in fianking positions, well traversed fi*om
enfilade fire, and in retired positions between the works or on
high ground. They are not in the works themselves as a rule -
(though the latter nearly always provide for the use of guns if
required), as in them their mobility is impaired and they are
Mkely to be silenced by a superior convergent artillery fire.

177. When the time for preparation is short, as in most battle- ^^^ ▼orks.
fields^ the decisive points are fortified by shelter trenches and
obstacles in lieu of regular redoubts ; localitie?, as before stated,

admit of at least some defensive arrangements in the shortest
time that may be available. It is very advisable in these hurried
cases to trace these hasty works like the stronger works that would
otherwise have been made, so that in case of time being unex-
pectedly to spare, they can be improved by widening and deepen-
ing their ditches and increasing the size of their parapets.

Execution of Works,

178. Some details of execution have been previously given, and
others will be found in the chapter on Siege works.

The following is a list of the tools carried by R. E. companies Tools supplied
and battalions of infantry : — in the field.

114

APPLIED FIELD FOBTIFIOATIOK.

Plan of
defences.

Fortified
pivots.

Reliefs.

Shelter
trenches.

Gun-pits, &c.

Tools.

Boyal Engineer

Company.

Army Corps.*

Battalion of
Infantry.

Picks -
Shovels

Spades . . -

Axes - . -

Hand-saws
Cross-cat saws -
Billhooks

Boring and crowbars -
Heavy hammers
Besides other articles.

180

130

606
606

32
495

22
250

74
128

150

50
4

Trenchwork by
an English
division.

It may be assumed for calculation that each battalion can
furnish two companies of 125 men each^ with tools distributed as
follows : —

For intrenching, 142; for sod cutting, 10; for clearing timber,
&c., 75 ; for brickwork, &c., 4; for reserve, 19. These numbers
leave 8 picks and shovels and 6 axes (pioneer's) for use in bivouac.
* For cutting brushwood, clasp-knives are useful.

Besides these, officers in charge of defensive preparations would
obtain as many tools as possible from the neighbourhood. For
works- in connexion with a siege, the siege equipment may
probably be drawn upon for extra tools.

The plan of the defences must first be settled by the com-
manding engineer in consultation with the general commanding.
Fortified supporting points, such as villages, Ac. and redoubts^
require a large proportion of skilled workmen for their construction.
The working parties of infantry for them must be told off, under
their own officers, with as many reliefs as the work to be done
may require. There should be a reserve of about 10 p. c.

Beliefs of four to six hours answer the best for excavators*
work, during which time 80 or 90 c. ft. of earth may be expected
from each man.

Shelter trenches for troops in the intervals are executed by the
regiments that are to occupy them, being laid out by their own
officers, who will have had general directions as to the ground they
are to occupy.

Gun-pits can generally be made by the gunners with the tools
carried on the umbers ; but many additional pits, &c. will be
required, for which special working parties must be told off, as
also for limber pits when necessary.

179. The following extract from the E. E. prize essay for 1875^
by Captain T. Fraser, B.E., will give an idea of what may be done
in a short time by a division : —

" It has been seen that with each infantry division, there would be about
" 130 engineer and 1,000 infantry sets of picks and shovels, and a division
" having to intrench itself in first line could generally be reinforced by half of

* There are 4 companies of Boyal Engineers to an army corps, and the tools of
of the B.E. field park are also included.

€(
C€
Ct

FORTiriCATION OF F081TI0NS. 115

'' the 4tli R. £. company with the army corps. This would make up the tools
** in round numbers to 1,200 sets (exclusive of the six sets with each gun, and

of about 2U0 spades for sod cuttin)^, which would be used with weir own

companies where most wanted).
These, with only a clear half or three-quarters of an hour for work, would Under one

give the power of making 2,400 paces of common shelter trench. With hour.

about an hour available we could throw up about 1,800 paces of common
*' shelter trench, and, say, 1,200 paces of the section shown in Figs. 6 and 7$
" Vh I.*

" With the prospect of not more than a relief of five hours, the same sections With oiu*

would be used, except here and there where bits of the breastworks shown relief.

in Fig. 9, PL I., might be best.

''Thus the division might in five hours throw up about 1,600 paces of
'' common trench, 1,500 paces of sections in Figs. 6 and 7> and at tne most
'' important points 400 paces of section in Fig. 9, the latter being traced to
*' form iaces and flanks.

'* Could we calculate on two reliefs, and if the gpround or localities provided Two reliefii.

more cover, we might, in the 1st rdief, use only 1,500 paces of Figs. 6 and 7, First relief.

and with the remaining 700 sets of tools begin 500 or 600 paces of the

section shown in Fig. 8, PI. XIII., placed in decisive situations so as to
'' become the faces and flanks of two or three redoubts.

In the 2nd relief the 700 sets of tools might be used to complete the Second relief.

redoubt sections to a height of 6 feet, while in the same relief fresh parties
" would work at the gorges, and dose or half close those that "required it.
'* Others would make field casemates (Fig. 8, PI. XIII.) in the works and help

to complete the traverses for which tongues would have been left.
The balance of the intrenching tools would be used in this relief to

complete any cover required, in addition to that thrown up in the first
" relief.

" With a third relief 250 to 300 diggers in the redoubt ditches would thicken Extra third
'' the parapets to 9 or 10 feet, and others would deepen parts of the trenches relief*
'' and blind them with logs or rails and earth. (Fig. 32.)

" In addition, any desirable improvements in the existing shelter trenches
'' would be carried out.

The divisional artillery would, in like manner, intrench itself according to Divisional
" the time available. artillery.

In the meantime the engineers, with the infantry in support and reserve. Supports and

would prepare anv additional gun-pits and position gun-batteries, would reserves.

provide cover for the supports and reserves, and work on the communica-
tions.

**The tools available, including those of the field park, would be more

numerous, in proportion to the extent of these works, than for those of the

first line."

Section 6. — Varieties of Fortified Positions.

180. These may be grouped under the two h^vAs pure defensive
and offensive defensive. The former includes : —

(a.) Lines of investment.

(ft.) Defence of the environs of a fortress.

(c.) Defile works, bridgeheads, and mountain passes.

(rf.) Intrenched camps, depdts, &c.
The latter applies to ordinary battlefields.

In all of these cases the fortification of the positions taken up,
whether in a straight, concave, or convex line, is applied in the
same way, viz., in providing a chain of tactical pivots, varying in
their strength and distance apart according to the passive or
active character of the defence.

* The original references have been altered to correspond with the plates of this
book.

CC
CC
CC

APPLIED FIELD FORTIFICATION.

Character of
defence.

Nature of
works.

Outpost
poBition.

Reserve
position.

Piecemeal
nature of the
works.

Artillery
positions.

Lines of Investment,

181. As the force investing a fortress has, especially in the case
of those having detached forts, to cover a large circle, the fortifi-
cation of the investing line as a means of economising numbers is
a great gain, enabling the defenders to be kept in check during
any attempt to break through the line of investment, until the
reserves shall have had sufficient time to be massed at the
threatened point.

As pursuit is forbidden by the guns of the fortress, the character
of the fight is purely defensive in its tactical object, and a very
free use must be made of obstacles along the whole front, espe-
cially as from the nature of the case the enemy cannot turn the
flanks, but must make a front attack. The supporting points must
be strong, of the nature of half-closed w^orks, and their distances
apart the lower limit before laid down (viz., about half a mile).

There should be a well-advanced outpost position occupying
villages, &c., of the nature of open works, with their garrisons well
sheltered from the distant fire of the fortress or forts, their main
duty being to give early information of sorties, &c., and to delay
the enemy sufficiently to give time for the main line to be
fully prepared. The outpost position must, therefore, in this case
be regarded as a post of observation rather than as a fighting
position. The troops are intended to retreat before they become
involved or mixed up with the enemy.

In accordance with the arrangements for all passive defence,
obstinate defence of the ground. is to be ensured by the fortifica-
tion of a second line of pivots in rear of the main position, of the
nature of closed works, which second line is to be regarded as a
new line of defence for' the troops to fall back upon. (^See
Section I., par. 137.)

The works in an investment, being from the first liable to
constant interruption by the enemy, must necessarily be of a
piecemeal description, built up and strengthened more and more
as time goes on. Thus the first object would be to ensure a good
shooting line and cover their front well with obstacles ; then to
select villages, woods, &c., as defensive pivots, and strengthen
them gradually in the order of importance given under that
subject ; field redoubts would be laid out where necessary to make
up for the absence of other pivots, and executed as men became
available for their working parties. Special attention would be
paid to keeping up thorough communication between all parts of
the investing line by roads and telegraphs.

The artillery with an army of investment being, at any rate at
first, the ordinary field guns^ they will be probably prevented by
the superior weight of the defenders' guns from being pushed
forward to any great extent ; a position in the second line, behind
the main shooting line, is the most generally suitable for the mass
of the artillery in this case, as from thence they can not only co-
operate in resisting sorties by flanking and frontal, direct and
indirect, fire from elevated positions in rear, but are well placed
for driving the enemy out ot the first line if he carries it.

VABIETIE8 OP FORTIFIED POSITIONS. 117

As the investment is a good case of a defensive battle-field,
only under rather stringent circumstances as regard<i necessity for
increased vigilance and preparation at all stages, with at the sama
time very Hmited choice of ground, a detniled plan of the German
position east of Metz, during the investment.in 1870^ is given in
Fl. XLV. (at the end of this volume). A note upon this position
will be found in Appendix C.

182. The arrangement of a purely defensive battle-field with the Defensive
advantage of choice of position would be similar in £i:enernl treat- ^ttl«-yel«l» «n
flient; it* a natural obstacle to protect the front were made use of,

as would usually be the case, the only precautifm necessary to add
is that the main shooting line should be within effective rifle
range (less than 600 yards) of the obstacle, the whole of which,
especially at its principal points of passage) should be swept by
linnkingand direct fire. Moreover, in proportion to the eflSciency
of this obstacle, the value of the first line would be increased,
and there would be less necessity for a strong second line. Nor
would the outpost position be so necessary except as a protection
to the defenders' communications across the obstacle, when these
are required ; the passage should be ensured by works in front
of the points of passage having the nature of half-closed works
(ie,, secure against surprise).

As the arrangement of the actual line in all the cases of purely
defensive positions is very similar to that just described under
*' Investment," it will not be necessary to repeat the details in
each case, but merely to note their peculiarities.

Environs of a Fortress.

183. A defensive girdle can in a similar way be drawn round
a fortress by the defenders, to keep the enemy at a distance, and
permit of the free action of part of the garrison in the field. This
position should be within artillery range of the place, which will
prevent an attack upon it from being ]>ressed home. In this case
the fortress acts as a secure base, and the troops in the open have
the advantage of possessing no impediments.

The necessity for a well-fortified line of pivots (field works,
villages, &c.), is here all the greater, as the numbers of the
defenders are not likely to be large in proportion to the extent of
the outer girdle line ; but they have the advantage of all parts
of the line being equally accessible to a central reserve.

Here, one strong shooting line is required, the fortress acting Arrangement
as a reserve position. The ordinary outposts for purposes of ®^ *^® '^®'''^®*
observation would be thrown out.

The line should be supplied with a large proportion of guns,
including amongst the number such of the fortress artillery as
can be mounted on travelling carriages, drawn from fronts not
likely to be attacked.

The character of the works should be half-closed, and the Character of
intervals may incline to the larger limits (tending to economy of ^^'^^•
the defensive force), owing to the power and range of the
defenders' guns, and the free and well-supported action of the
reserves before alluded to.

118 APPLIED FIELD FOBTIFIGATIOK.

The nature of the defence making the pivots all important^ few
fortresses of any importance at the present day would be without
a girdle line of forts of strong profile, giving one another artillery
support, and making it easy to hold by ordinary hasty field
fortifications the intervals betweea them. (See Chapter lY. on
Fortresses and Forts.)

Unfortified towns of importance may have to be protected by
field works (^.^., Washington, Kouen, &c.).

Defile Works and Bridge-heads,

184. The general idea of a defile is that of a narrow passage
over a natural obstacle. Defiles may either occur —

1. In the passage of rivers, marshes, &c, in which water is the

obstacle. .

2. In the passage of mountain ranges, &c., in which the relief

and character of the ground is the obstacle.

In either case the principles of arrangement of the works are
the same, the only points of difference in their execution being
such as depend on the actual locality in each case, such as the
mechanical means of barring the defile, or the materials available
for constructing the works.

The subject may be divided, as to defensive arrangements, as
follows : —

A. Denial of the defile to the enemy's use.

B. Securing the defile for our own use.

185. A. Denial of passage to the enemy.

(a.) Preventing the enemy from passing the defile.
(6.) Preventing his deployment after passing.
Obstructing (a,) The chief application of this case is to a mountain pass,

moSfain ^^ obstruct the passage a fortified position must be taken up in

pass. the defile, consisting, in the first place, of obstacles across, or

destruction of, the road at the most favourable point for these
purposes, and ^vhere such obstacles can be best defended by fire.

This road-barrier should be unseen by the enemy from a dis-
tance, and defended by the smallest possible force, consisting
usually of infantry under cover, so placed as to flank its front.
Their own position should be secured by obstacles connected with
the barrier and arranged so that th^y cannot be outflanked. The
road leading to the barrier should be swept by guns placed in
concealed and safe positions along its general prolongation. A
turn in a defile appears to be the most favourable position for an
obstruction to fulfil the above requisites. In defiles of great
length several such positions might have to be taken up.

Fig. 1, PI. XLL, gives an actual example. When the Viceroy
Euglne Beauharnais was following the Archduke John, in 1809,
through the Carnic Alps, he found his road barred at Midborgetto
by three companies, with 10 guns, occupying blockhouses and
batteries, as here shown. He was unable to advance, until, with
much labour, guns had been taken up on to a spur of the heights
on the opposite side of the stream. 1 his was accomplished in the
night ; and troops were also sent on to the heights overhanging the
post itself. The following day, after a sharp combat, the works
were stormed. They were ill covered by obstacles : there was no
line of abatis as shown in the figure.

F. F. PldK? XEL

YABnSTlXS OF FOBTIFIED POSITIONS. 119

(b.) To prevent the enemy deploying at the mouth of the defile. Prevention of
This is applicable to the case of any defile. The mouth of the defile deployment.
should be blocked as efficiently ae possible by material obstacles ^^^ ^^^'
or by demolitions, and the defile enfiladed by batteries placed in
its prolongation, if possible, on commanding ground, and within
effective range of the furthest point that can be seen. If
the obstacle has been passed, the enemy in deploying must be
met by a converging fire of rifles and guns at effective ranges ^^'
£rom a concave shooting position, arranged as before for passive Girdle line.
defence, enclosing the mouth of the defile. The pivots of this line Cbanuster ol
should have the character of closed or half-closed works. (Fig. 2, P^^®^-
PL XLI.)

A second line of works may, as a rule, be dispensed with, as
the enemy is at a great disadvantage as regards position.

186. B. Securing our own passage —

(a,) In retreat
(&) In advance.

In both cases a position on the enemy's side must be held.

(a,) To secure the passage to a force in retreat, as much of the Retreat,
ground in front of the mouth of the defile must be secured as wiU Defile work.
enable the retreating force to effect its passage under the pro-
tection of the rearguard. For this purpose a fortified girdle Une,
with its flanks resting on the obstacle, should enclose the neces-
sary space. Its length must depend on the strength of the rear Length of
guard, which would be from about one fourth to one sixth of the &^^^ ^*'^®-
whole force (varying with the numbers and proximity of the
pursuing advanced guard), distributed along the line at the rate
of three to four men per pace at most. In any case the distance
of the girdle line from the mouth of the defile should be sufficient
to prevent the enemy's artillery &om enfilading it; assuming 3,500

iards as the extreme effective range of their guns, and that the
itter are kept at a distance of 2,000 yards from the girdle line,
the distance of the latter from the defile would be about 1,500
yards. If the formation or clothing of the ground afforded much
concealment, the distance might be smaller.

The character of the pivots in the girdle line would be that of Character of
half-closed works. They would usually be fortified localities, or, ^^^ ^^•
in default, earthworks of slight profile, as the conditions of the
case do not argue much time to spare.

The retreat of the rearguard itself must be similarly secured Keep of defile
by a smaller fortified position immediately in front of tne defile,
capable of defence by the reserve of the rearguard. This may Nature^f
consist of a single fortified village, or a continuous line of earth- ^®'^s-
works, with its flanks leaning on the obstacle, or even of a single
earthen redoubt commanding and barrmg the approach. The
latter should be a half-closed work (the profile as strong as pos-
sible, and having bomb-proof cover), as best suited to liability
to enveloping attack and to preventing its being held by the
enemy if captured. The available garrison for a defile keep might
possibly be a battalion.

120

APPLIED FIELD FOBTIFIOATION,

Case of a river.

Special con-
ditions of the
above works.

Flanking posi-
tion.

Case of moun-
tain pass.

Offensive defile
works.

Character and
arrangement
of works.

Defile keep.

Finally, preparations should be made for barricading or de-
stroying the entrance to the defile after the retreat of the last
body of defenders, and a debouch* position may be prepared on
the rear side as just described in para. 1 85.

187, In the case of the obstacle being a river, the distance of
the girdle line must be specially arranged with a view to pro-
tectino" the bridge or bridges from destruction by the enemy's
distan^t artillery fire, and the keep should as far as possible conceal
the bridge and cover it from fire.

The girdle line of works, and also the defile keep, should be
efficiently flanked (as far as the width of the river will allow) hj
artillery and musketry, the former especially, posted on ihe

hither bank. ^ ...

In the case of a mountain pass the flanking positions above
mentioned are evidently not so readily obtained, but any accessible
places on the heights on either side of the mouth of the pass
should be occupied with the same object, always providing there
is direct and secure retreat from them and a good obstacle in front
of them.

188. (6.) Securing our own advance through a defile in presence

of an enemy.

Here the fortifications are very similar in principle and arrange-
ment to those just described for covering retreat. The object is
to enable the advanced guard to hold suflBcient ground on the
further side to admit of the uninterrupted passage and deployment
into order of battle of the main body ; but offence being the object
greater freedom of arrangement is desirable.

For this purpose, as before, a girdle line of fortiSed pivots is
required in advance of the mouth of the defile, at a distance
depending on the numbers of troops to be deployed, but otherwise
not less than that named for defile works to cover retreat. The
distance can be fairly arrived at by a distribution of the infantry
available for the shooting line and local reserves (including the
advanced t^uard) along the girdle line at the rate of two to three
men per pace, as before mentioned. When tfce main body fol-
lows closely on the advanced guard, the smaller number could

safely be taken.

The pivots, as before, consist of fortified localities or earthworks,
of the nature of half-closed works. Their distance asunder should
incline to the smaller of the normal dimensions already laid down,
as the advanced guard (naturally weak in reserves, on account
of the leno-th of the line it will have to hold) has to maintain itself
till the main body shall have crossed.

The barring of the intervals by obstacles is here not of such
importance, if, as is most probable, the gradually increasing sup-
port of the main body can be relied on ; moreover, the unimpeded
advance of the latter has to be provided for at all points where
the ground is favourable ; the possibility, however, that offensive
defile works might have to be used to cover retrograde movements
as well, makes it advisable that the intervals should only be such
as are .suited to battalion, or, at most, brigade advance.

A defile keep is here also necessary.

122

APPLIED FIELD POBTIFIOATION,

Doable bridge-
bead.

Simple bridge-
bead.

Manoeuyring
bridge-head.

Diippel bridge-
head.

for instance, when a river runs parallel to the line of com*
munications, the works are similarly arranged on both banks,
and constitute a Double Bridge-head, In the latter case the
central point or kernel of the defence is at the bridge itself,
whereas in the former the central point is somewhere in rear of
the bridge, where the reserves would be.

When the works are intended simply to protect an existing
bridge from demolition or occupation by the enemy, the bridge
being useful for reconoitring purposes by small bodies, they are
called Simple Bridge-heads, and may consist of a single work,
half-closed at the gorge placed on the principal road. It most
be connected by means of obstacles with the stream to prevent
its rear from being turned ; the thoroughfare should pass through
a barrier in the obstacle, and not through the work itself.

Works of this kind should be capable of resisting till the
arrival of assistance, or until the bridge may have been rendered
useless to the enemy, for the time at least, by demolition.

When the works are intended to cover the advance or retreat
of large bodies of troops, the arrangements before described
(girdle line, &c.) are necessary, and the whole system is termed
a Manoeuvring Bridge-head,

As an instance of a single bridge-head, Phite XLIII. shows the
Danish works at Diippel, by which, in 1864, they still kept a foot-
ing upon the mainlana of ScUeswig, when their army had been
forced to retire before the Austrians and Prussians into the island
of Alsen.

The first line consisted of 10 detached works^ of which Nos. I.,
II., IV., VI., VIII., IX., and X. were closed at the gorge. Their
parapets had a command of 12 feet, and were 15 feet thick. Their
ditches were 15 feet deep and 15 feet wide at the bottom, and
were provided with palisades. There were also fraises in the
counterscarp, but the ditches were unflanked. In the intenor o£
these works there were blockhouses as keeps, not sunk sufficiently
low to be hidden from view from the &ont, and oonseauently
easily breached. The other three works were lunettes witn xnli-
saded gorges, and of rather less command. The communications
between the works were for the most part trenches of weak profile.
In front of them were wire entanglements, pits, and stakes as
obstacles; but these seem to have hindered the sorties of the
defenders more than they hindered the advance of the enemy.

The second line was begun as soon as the Danes found that the
long range of rifled guns would allow the Prussians to enfilade the
left part of the first line from batteries on the other side of the
Wenningbund^ but there was no time to finish it.

The keep of the bridge-head opposite Sonderburg had the same
profile as the works of the first line, with the addition of abatis
m front of the counterscarp. The final assault of the Prussians
upon this position is noticed in Appendix No. 4.

Use.

Intrenched Camps, Depdts, ^c,

190. When it is necessary to keep a large force, capable of
exercising an influence on the campaign, at any particular pointy
ready to strike a blow in any direction^ or to give shelter to an
army that has been worsted in the fields and to enable it to
reorganise^ the position chosen must be maintained by means of
fortifications^ and forms what is termed an intrenched camp.

TASIETIE8 OF FOBTIFIED POSITIONS. ' 121

1l89. The<)hierflpp]ication of the foregoing occurs in the passage
oi rivers.

The portion of the course of a river at which a crossing is to be Bridge-head,
effected having been selected with a view to strategical coneidera-
tioDs, the actual point of passage has to fulfil two classes of Clwice of
requirements, vi^. : — tactical, and technical, JJ^ ^**'

The tactical I'equirements are : —

1. Convenient and hidden communications to the river. The hither

-2. Space near the site of the bridge for bridge making, ^'*'*"

approach of troops, &c.
S, Command of the far bank from the near to favour the effects

of fire supporting the operation, with facilities for bringing

a flanking fire also to bear.
4. Facilities for passing the advanced guard over the river, and

fords for cavalrv.

ft'

5. Ground on the other side favourable for the construction of The fbrther

the girdle line of pivots. ^'•"'^

6. Space for deployment, protected from view and fire.

7. Open ground in front of the girdle line favourable for the

advance of large bodies of troops.

The technical requirements are concerned with the actual con-
■struction of the bridge, and will be found treated at length in the
chapter on ** Military Bridges.'*

The tactical requirements are usually best fulfilled by choosing
a re-entering bend as the actual point of passage ; as here the near
side is more likely to be higher than the further, affording good
artillery positions and probably a concealed approach; also by
placing artillery on the flanks of the bend its fire crosses in front
of the immediate point of passage and flanks portions of the
girdle line. 1 he latter in its turn need not be of so great extent^
and its flanks are secure. On the other hand, a very deeply re-
entering loop is not desirable as regards offensive movements from
the bridge-head, as the debouching troops are shut up in a small
epaee under a converging fire, .and are to some degree in the
unfavourable situation pf troops emerging from a defile.

It therefore appears that though a re-entering bend is on a
small scale desirable for the bridge itself and for the bridge-head
keep, yet the dimensions of the bend must not be such as to
cramp and restrict the further advance, which depends also on the
nature of the country beyond. The point of junction of a
tributary stream with the main channel, if suitable in other
respects, offers considerable advantages in the case of floating
tridges, in the way of concealing the construction of rafts,
booms, &c., which are afterwards floated down into position.

Fig. 1, PI. XLIL, gives an example of a bridge-head suitable
for offensive purposes, the defenders having complete possession
of the near bank.

When the latter is the case, the river running perpendicularly
to the line of communications, the arrangements of works con-
stitutes what is called a Single Bridge-head. When the power Single bridge-
of resisting attack on both sides of the stream is desired, as, l^ead.

42642, I

•Ifn

TABIETIE8 OF FOBTIFHSD POSITIONS. 123

They are usually placed on or near some important line of Sltnatioii.
communicatioiiy and thus a mancBUvring double bridge-head is
usually of sufficient size to form at the same time an mtrenched
camp.

Here would generally be stored supplies of different sorts, both

of food and war material.

The main principles of construction of these camps or dep6ts Frinciplet of
^r^. ■ ooottmotioD*

1. The enclosing of sufficient space to receive the army.

2. The possession of ample resources for maintenance and

equipment.

To ensure these conditions^ the girdle-line of pivots must be Ditpodtioii
at such a distance from the centre as to keep the enemy's °^^'®***
artillery out of range of the camps and stores, the sites of which
should be hidden from his view by the form of the ground.

The girdle-line must be capable of being held by the minimum
of troops against determined attacks, and shoula be strong in
artillery. At some points there should be facilities for assuming
the offensive, but the general arrangements will be more for the
passive defence. An inner line of works at favourable points
would be of service, especially when the outer circle is very
large.

The works should be strong and generally half-closed. Their Nature of
distance from the selected camping grounds should be at least a P^^^'ts.
mile, so as to keep the enemy's guns at a distance of two miles
from the latter. Probably a greater distance than this would be
necessary in most cases.

The spaces necessary for encampments are given in the officii

book of instruction on the subject ; but it may be roughly stated

that the necessary space would be from 15 to 20 acres per 1,000

men when closely packed, and nearly double when the different

regiments, &c. are spaced liberally, as is usual in standing camps.

As a rule, infantry camps should be placed in first line, and
other arms * in another line distant from 100 to 300 paces from.
ihe first.

In the case of encampments within a fortified line, as the
arrangement of the camps with a view to battle order is not of
such great importance, and in order to prevent too great an
extension of the girdle-line, the total circuit of the camps should
be as small as possible. It may be assumed for rough calculation
that an army corps of 30,000 men could encamp within a circuit
enclosing from 1^ to 2 square miles.

To protect supplies and material, even after the fall of the Keep,
girdle-line, there should be a central fortified point, which may
consist of a continuous line with enclosed redoubts at intervals.

If a village or town is the central point, it should be fortified
etroDgly in the usual way, unless of too great extent, in which
case a line of detached works may be constructed outside it in the
best tactical positions.

I 2

124

APPLIED FIELD FORTIFICATION.

The attack. :

The Offensive Defensive.

191. Since this line of action is confined to battle-fields, and
argues that the defenders are not very much inferior to their
opponents^ the works^ though similar in general arrangement and
principle to those described for defensive battle-fields, will in
detail consist chiefly of the more hasty kinds, such as shelter
trenches and gun-pits, with large and clear intervals left for
advance in force. Occasionally (as happened in the Americ-an
civil war) a concealed offensive movement to a flank may precede
the enemy's attack, fortifications enabling the defenders to guard
their original front with a very few men.

On the purely offensive the application of fortification is
naturally very limited, and may consist in enabling an advanced
guard to hold the enemy in check until the main force has had
time to come into action, or in the fortification of important points
on a possible line of retreat.

Section 7. — Attack and Defence of Field Wobks.

192. The attack may be made either by —

A. Storming;

B. Surprise ; or exceptionally by

C. Cannonade only.

Storming,

193. The attack should be preceded by as full a reconnaissance
as possible, to ascertain the best line of approach^ the strength of
the garrison, and the numbers and positions of the outer reserves.
The officer commanding the engineers concerns himself with the
details of the works, considering the best points of attack, the
obstacles to be encountered, the strength and composition of the
working parties, and the tools they must carry. The officer in
command of the artillery looks to the best positions for his guns
with respect to the following points : —

(a.) To enfilade the lines^ especially such as have trenches in
riear of the parapets.

(h,) To fire on the ground behind the lines with a view to
searching the roads of approach of the outer reserves.

(e.) To avoid, as far as possible, the necessity of moving the
guns.

As an introduction to the attack, the enemy's outposts must be

attack, driving driven in sufficiently far to allow of the construction of the

m outpos . batteries or gun-pits on the chosen positions without exposure to

the enemy's riflemen.

Periods of The attack which follows may be divided into four periods,

Attack. yiz^ . —

1. The cannonade.

2. The advance of the storming colunms to the glacis.

3. The storming of the parapets.

4. The capture of the interior and securing the works against

recapture.

Beconnais-
usance.

Introductory

ATTAOK AND DEFBNGG OF FI£LD WORKS. 125

194. A heavy converging artillery fire from a superior number Fl«t period :
of piecesj at a range not exceeding 2,000 yards, and less if prac* ^« ctnnomide.
ticablcj is essential to the success of the attack.

The objects of the cannonade are : —

(a,) To reduce to complete silence the artillery in the works or To silence the
in the intervals which may be directed on the attacking troops, utOlery.
especially those which flank the near approach to the works. If
the guns are found to have been withdrawn under cover into gun-
recesses and blindages, efforts must be made, by indirect and
other fire, to destroy the platforms, to choke the embrasures, and
generally to render the gun-portions unserviceable.

(b.) To damage the works. Complete destruction of earthen To injure the
parapets cannot be effected by the fire of field guns, although ^o'*^-
with the smaller profiles (under 9 fr. thick) a breach can be made
in any one spot by a concentrated fire of many guns on it.

The principal object, therefore, is to cut down the crest and to
produce irregularities in the superior slope, destroying loopholes
and other means of covering the defenders' heads, and making
the parapets inconvenient for use during the close fight. A work
dami^ed by a heavy fire will always impair the confidence its
defenders may have in its powers of resistance.

The destruction of the escarp, to facilitate scaling, is effected by
the indirect fire of shells grazing the crest of the glaci:?. If the
works are sufficiently well known, gates and ])ali!iades at the
goi^es can be destroyed also by indirect fire.

Obstacles in the foreground can only be damaged if exposed to
view. It is difficult to ])roduce any real effect on abatis, pits, or
wire entanglement. The former, it' very dry, may be set on fire,
but it must not be burning when the assault takes place.

(c.) To harass and infiict loss on the garrison. As during the To i^iake the.
cannonade the garrison will lie close under the parapets and in ff"™^**'
the blindages, they are chiefly to be got at by an enfilading fire,
which has the advantage that it can be kept up until the stormers
are very close to the works. By keeping up an incessant fire the
garrison are to some extent prevented from showing themselves,
and from observing and resisting the approach of the stormers.

When the stormers h&ve arrived so close to the works as to be
in danger from the fire of their own artillery, the latter must be
directed against the flanking and supporting works, and on the
positions of the outer reserves.

195. The advance of the infantry is effected in the manner Second period:
already described, the crisis of tlie fire-combat occurring as close J^J^^jL
to the works as possible.

Accompanying the supports would be the worMng parties,
provided with tools and expedients for surmounting obstacles,
and in rear of these again is the main body of the stormers.
A second attacking line follows, at a distance of 300 to 500 yards
from the first, to engage the*outer reserves.

When the rapid independent fire of the assailants has begun
to tell, and the fire from the parapets becomes slack, a rush

124

APPLIED FIELD FORTIFICATION.

The attack. :

The Offensive Defensive.

191. Since this line of action is confined to battle-fields, and
argues that the defenders are not very much inferior to their
opponents^ the works, though similar in general arrangement and
principle to those described for defensive battle-fields, will in
detail consist chiefly of the more hasty kinds, such as shelter
trenches and gun-pits, with large and clear intervals left for
advance in force. Occasionally (as happened in the American
civil war) a concealed oflFensive movement to a flank may precede
the enemy's attack, fortifications enabling the defenders to guard
their original front with a very few men.

On the purely ofiensive the application of fortification is
naturally very limited, and may consist in enabling an advanced
guard to hold the enemy in check until the main force has had
time to come into a<ition, or in the fortification of important points
on a possible line of retreat.

Section 7. — Attack and Defence op Field Works.

192. The attack may be made either by —

A. Storming;

B. Surprise ; or exceptionally by

C. Cannonade only.

Storming,

193. The attack should be preceded by as full a reconnaissance
as possible, to ascertain the best line of approach, the strength oi
the garrison, and the numbers and positions of the outer reserves.
The officer commanding the engineers concerns himself with the
details of the works, considering the best points of attack, the
obstacles to be encountered, the strength and composition of the
working parties, and the tools they must carry. The oflGicer in
command of the artillery looks to the best positions for his guns
with respect to the following points : —

(a.) To enfilade the lines, especially such as have trenches in
rear of the parapets. *

(b.) To fire on the ground behind the lines with a view to
searching the roads of approach of the outer reserves.

(e.) To avoid, as far as possible, the necessity of moving the
guns.

As an introduction to the attack, the enemy's outposts must be
attack, driving driven in sufficiently far to allow of the construction of the
m outpos 8. batteries or gun-pits on the chosen positions without exposure to

the enemy's rifiemen.

The attack which follows may be divided into four periods,
viz. : —

1. The cannonade.

2. The advance of the storming colunms to tlie glacis.

3. The storming of the parapets.

4. The capture of the interior and securing the works againet
recapture.

Beconnais-
■sance.

Introductory

Periods of
attack.

ATTAOK AND DEFENGG OF FI£LD WORKS. 125

194. A heavy converging artillery fire from a superior number First period :
of pieces^ at a range not exceeding 2^000 yards, and less if prac* ^« ctnnoiwde.
ticable, is essential to the success of the attack.

The objects of the cannonade are : —

(a.) To reduce to complete silence the artillery in the works or To silence the
in the intervals which may be directed on the attacking troops, ^rtOlery*
especially those which flank the near approach to the works. If
the guns are found to have been withdrawn under cover into gun-
recesses and blindages, efforts must be made, by indirect and
other fire, to destroy the platforms, to choke the embrasures, and
generally to render the gun-portions unserviceable.

(p.) To damage the works. Complete destruction of earthen To injure the
parapets cannot be effected by the fire of field guns, although ^<*«'*^'
with the smaller profiles (under 9 ft. thick) a breach can be made
in any one spot by a concentrated fire of many guns on it.

The principal object, therefore, is to cut down the crest and to
produce irregularities in the superior slope, destroying loopholes
and other means of covering the defenders' heads, and making
the parapets inconvenient for use during the close fight. A work
damaged by a heavy fire will always impair the confidence its
defenders may have in its powers of resistance.

The destruction of the escarp, to facilitate scaling, is effected by
the indirect fire of shells grazing the crest of the glacis. If the
works are sufficiently well known, gates and ])ali:iades at the
gorges can be destroyed also by indirect fire.

Obstacles in the foreground can only be damaged if exposed to
view. It is difficult to produce any real effect on abatis^ pits, or
wire entanglement. The former, it* very dry, may be set on fire,
but it must not be burning when the assault takes place.

(c.) To harass and infiict loss on the garrison. As during the To i^iake the.
cannonade the garrison will lie close under the parapets and in ff"f™o**«
the blindages, they are chiefly to be got at by an enfilading fire,
which has the advantage that it can be kept up until the stormers
are very close to the works. By keeping up an incessant fire the
garrison are to some extent prevented from showing themselves,
and from observing and resisting the approach of the stormers.

When the stormers hfeve arrived so close to the works as to be
in danger from the fire of their own artillery, the latter must be
directed against the flanking and supporting works, and on the
positions of the outer reserves.

195. The advance of the infantry is effected in the manner Second period:
already described, the crisis of the fire-combat occurring as close J^J^j^nr.
to the works as possible.

Accompanying the supports would be the working parties,
provided with tools and expedients for surmounting obstacles,
and in rear of these again is the main body of the stormers.
A second attacking line follows, at u distance of 300 to 500 yards
from the first, to engage the'outer reserves.

When the rapid independent fire of the assailants has begun
to tell, and the fire from the parapets becomes slack, a rush

126

APFLI£D FIELD FOBTIFICATIOK.

Ditches.

Abatis.

Palisades and
fraises.

Chevaux-de-
frise.

Entanglements
and military
pits.

must be made for the ditches of the works. This should be done
by a portion of the attacking line^ in order that the fire on the
defenders may not cease altogether ; the working parties advance
with them to clear away obstacles. If none are encountered on
the glacis^ the stormers rush at once into the ditches ; if other-
wise, the obstacles must be first removed by the working parties^
or gaps about 25 paces wide must be made for the passage of
the stormers. All this time some of the assailants keep up a
fire on the defenders of the parapet whenever they show them-
selves. Any flank attacks now made by the defenders' outer
reserves must be met by the troops detailed for the purpose, so
that the storming columns may be uninterrupted in their work.

The passage of the ditches can be facilitated by bringing up
with the assaulting column sacks of wool, shavings, &c., or bundles
of hay and straw, or fascines ; these thrown into the ditch will
fill up a portion and assist in forming a passage over it. The
fascines in this case may be short, cut into 6-feet lengths, so that
a man can run over rough ground carrying one or two of these
fascines besides his arms and accoutrements.

An abatis of green timber is most diflficult to demolish ; artillery
fire will have produced little effect on it, and the only way of
forcing a passage is to work with axes at the stakes by which
the trunks of the trees are fastened,, and then by means of ropes
to draw out disentangled portions. To effect this under fire is
scarcely practicable. Lengths of powder-hose filled with gun-
cotton discs, or granulated gun-cotton, and thrown to the abatis
and detonated, will clear away some portions of the obstacle. If
the abatis be made of dry wood, breaches may be made in it by
this means. If dry, the abatis may be demolished by firing
incendiary shells into it, or applying petroleum and setting fire
to it.

Palisades and fraises may be destroyed by using axes, if the
flank fire protecting them can be subdued. Powder bags will
make casual gaps in them, and pipes or hose filled with gun-
cotton and detonated will cut them down level with the ground.

Chevaux'de-frise can only be removed by being roUed over to
one side, and if they have been secured together by chains or
stout wire it takes a considerable time to clear them away.

Entanglements and military pits can be surmounted by making
roadways over them with doors, wide planks, hurdles, or bays of
boarded fencing.

If the ditches are defended by caponiers or galleries, the
assailants endeavour to drive the defenders from the loopholes
by inserting firebrands, and the moment a loophole is cleared
plugging it up with wooden wedges or bags of hay, &;c. ; or the
caponier or gallery may be breached with explosives. In the
case of sunken caponiers, the loopholes of which are close to the
bottom of the ditch, fascines, &c. can be thrown down in front
of them to mask them.

196. By the time the obstacles have been surmounted the
main body of the stormers will have arrived^ and the assault

ATTACK AND DEFENCE OF FIELD WOBKS. 127

must now be given with energy, on as large a front as possible* Third period:
The stormers^ after having assembled in sufficient numbers in "■*"^*<*^*^«
the ditch or on the berm, rush over in a body, and mix with P**^*®"*
the defenders in hand-to-hand encounter, following them pell- Fonrth period;
mell into the retrenchment or keep if there is one. If, before ?$i^ *^*
the final rush, the defenders have left the parapets and unmasked
the fire of the keep or retrenchment, the assailants lie on the
superior slope and oppose the fire whilst an attempt is made to
open the keep by means of explosives, or by main force. This
wJU depend on the nature of the keep. If it consists of a block-
house, the sappers with gun-cotton, &c. should advance against
the dead angles and endeavour to breach it, or to force the
defenders from the loopholes, as before mentioned in the case of
caponiers in the ditch. If they can manage to get on the roof
of the blockhouse by means of ladders, they may lodge mines
beneath the earth covering and on the top of the roofing baulks.
In case of mines being suspected to exist in the interior of a
work, the stormers should retire to the berm or ditch, and an
officer of engineers must endeavour to discover and cut the hose
or wires leading to the charge.*

197. After capture the magazines must immediately be ^^^' capture,
examined to see if they are prepared for explosion; the guns

of the work are turned on the retreating defenders, the entrances
on the gorge side are closed and the bridges torn down, and
every preparation made for receiving an attack from the rear ;
the parapet of one of the former front faces is cut through to
form an entrance. If the work is half-closed by a stockade,
shelter trenches should be immediately thrown up behind it to
give cover iigainst the enemy's artillery ; if by a slight parapet,
this must be strengthened by cutting a trench in rear and heaping
the earth up agftinst the interior slope, to form a fresh interior
slope.

If the work is operiy or the gorge defence has been destroyed,
banquettes may be cut in the exterior slopes of those faces from
which a fire can be brought to bear on the enemy, until the
slackness of his fire enables the new defenders to make a fresh
gorge parapet.

198. If the work cannot be held the guns should be made Demolition of
unserviceable, the magazines blown up, blockhouses destroyed, ^fe^<^-
platforms broken up, and gun-banks cut away.

199. To find the enemy unprepared is always so important a Attack by
factor in the chances of success, that every attack by main force Boiprise.
should if possible be made suddenly and without letting the
enemy know of it; but sometimes, under cover of weather, or

when the defenders are much dispirited and their outpost duty
badly performed, or when immediate support of the work by
outer reserves is not forthcoming, an attack by a comparatively
small force may be made with considerable chance of success.

* See, in Appendix D, the orders issued for the assault of the works at Diippel.

128

APPLIED FIELD FORTIFICATION,

Attack by
cannonade.

Obviously in this case silence and secrecy are essential:?, and the
advance must be made without firing a shot.

200. In some cases the defenders may be forced to evacuate
their works or to capitulate by a cannonade only, effected by an
overwhelming superiority of artillery, followed, perhaps, by a
heavy fusilade from swarms of sharpshooters well ensconced in the
neighbouring ground. The circumstances which render such a
course likely to succeed are a depressed state of mind of the
defenders, a great inferiority of strength, or badly constructed
works, &c. The mode of proceeding is similar to that described
for the preliminary cannonade of an actual assault.

Against sur-
prise.

Against
storming.

first period :
the cannonade.

Second period :
advance of the
enemy's in-
ftntry.

The Defence,

201. Vigilance and a well-organised roster of duties, especial-
attention being paid to the outposts and patrols, are the best
security against surprise.

At night the barriers are shut, entrance of the patrols, &c. beiiig^
effected at one only. On the first alarm all should be at their
posts, and the guns loaded with case, ready to greet the enemy
with volleys. At daybreak especially the guards must be on the
look-out, this being the most probable time for an assault.

202. The preparations against an attack by storm may be
divided into four periods corresponding to those of the attack.

Advanced bodies of good riflemen should be posted in sheltered
and concealed places to keep the enemy's artillery at a distance
as long as possible, and to pick off the enemy's reconnoitring
oflScers. When these riflemen are obliged to retire on the outer
reserve by superior forces the enemy's cannonade commences..
The commandant of the work^ and the officers in command of
the artillery and infantry, watch the enemy's aSvance. A few
selected good shots from the garrison man the parapets, especially
at salients, and fire on officers and small bodies that venture too
close. The guns join their fire to that of the artillery of the outer
reserves to oppose the enemy's artillery as it comes into action ;
if greatly overmatched the guns in the works are run down into
the blindages. The infantry told off to the parapet sit or lie on
the banquettes of those faces which are not exposed to enfilade or
reverse fire. The defenders of the flanks and gorge keep close in
their blindages until the near approach of the enemy. The
reserve is kept under cover in the rear trenches and blindages.

203. As the enemy's infantry advances to within effective^
range (about 500 yards), the front faces are manned and fire oa
them. The guns are run up and open on the main bodies of the
workmen and stormers, as soon as they arrive within 1,500 yards r
the accurate knowledge of ranges gives the guns of the defence a

*great advantage.

The guns all concentrate on the nearest column first and then
on the others in succession, regardless of their own losses.

When the storming columns arrive within 300 paces, the flanks
and gorge must be manned, and support given by the former \x^

ATTACK AND DEFENCE OF FIELD WORKS. 129

adjacent works which may be eimilarly resiBting attack. The
guns continue their fire at all hazards. The reserves inside the
^ork leave their coyer^ and get rendy to resist the assault The
fougasses, if nny^ are sprung as the enemy nrrives within their
range. W'hen he reaches the glacis the outer reserves attack,
and oppose the penetration of the intervals between the works.

20^, When the enemy is in the ditches, hand grenades nnd Third period:
fiheJb are thrown over the parapets ; the defenders of the parapets ^^* *f ^*
fire unremittingly on the enemy's riflemen and on stormers not yet ^^~
in the ditch. All the defenders are ready with bayonets fixed to
resist the stormers, the guns fire as long as there is a gunner and a
round of ammunition left.

The inner reserve are loaded and ready to fire in case of the
retreat of tbe defenders of the parapet.

If the enemy succeeds in getting in and there is no keep, he Fourth period:
must be charged by the reserve, the beaten defenders of the J^^^*
parapet clearing away quickly to either fiank of the gorge to allow
the reserve to act freely by fire and bayonet. The outer reserve
may send assistance.

If there is a keep or retrenchment, the reserve must take care
to avoid a mSl^, and should retire rapidly towards the gorge, un-
masking the fire of the keep. On no account must the defenders of
the parapet or the reserve retreat into the keep ; it is best if there
be a place of assembly for them in rear of it.

After the fire of the keep has taken effect, the defenders may
make an attempt to drive the enemy back again over the parapet ;
or if a retreat be necessary, the keep covers that of the garrison of
the work, and, finally, that of the defenders of the keep is covered
by the outer reserve.

205. Any attempt at recapture of a work should be made Attempt at
immediately to prevent counter preparations of the enemy. recapture.

After the repulse of an attack, all damages must be rapidly After repulse
repaired, ammunition, &;c., replenished, and the garrison* should be ^^***II^'^'
strengthened, but not relieved, by fresh troops ; the outer reseryes
would assume the offensive, to complete the enemy^s defeat.

206. In attacking and defending posts other than earthen Attack and
redoubts, the same general rules apply ; but there is generally ^^^/^.
more work for special troops in the shape of demolitions and lages, &rms,
making walls, &c. defensible. &c.)

Section 8. — Hasty Demolitions.

207. Hasty demolition in the field is generally effected by
means of gun-cotton, whiclris about four times as powerful, weight
for weight, as gunpowder, and does not require tamping* in the
same way.

Gun-cotton is used in the form of cylindrical discs, or of flat
slab;?.

*** Tamping is covering the charge oyer with earth or other material so as to con-
fine the gases from the ppwder at the conmiencement of the explosion, and thus folly
develop their force in the intended direction.

130

APPLIED FIBLD FOBTIFIGATIOy.

Discs.
Slabs.

Fuze.

Detonator.

Bxploding
gunpowder.

Various de-
molitions.

Stockades.

Gates.

Walls.

Woodoi
bri4g««

The discs weigh about 1 oz. each with a diameter varying from
I" to 1}'^ or 9 oz. each with a diameter of 3'^

The slabs nre about 6 inches square and about 1 inch or 1^'^
thick, and weigh 1^ to 2 lbs.

The discs and slabs can either be used singly, or threaded or
sewn together in any number.

Gun-cotton is usually stored damp for safety, and as long as
a certain proportion of the charge is thoroughly dry, the explo-
sion is not affected by the dampness of the rest.

Explc^ion is ensured by means of various kinds of detonators,
fired either by simple fuzes or by electrical machines.

The ordinary fuze employed for demolitions is known as
Bickford's, and consists of a train of gunpowder enclosed in seyeral
coatings of thread and tape ; it bums at a rate not exceeding

4 feet per minute.

Fig. 3, PL XLIV., shows an ordinary detonator to be used with
Bickford's fuze.

The detonator is inserted as far as the point a into a hole in
one of the dry discs or slabs composing the charge.

Gunpowder is generally exploded by Bickford's fuze, or if this
is not to be got, by a powder hose. The latter is made of strips
of strong linen sewn together. It is made in lengths, filled with
powder and sewn together as required ; the diameter of a filled
hose is usually from ^'' to V\ Its rate of burning is from 10 to
20 feet per second.

208. A single stockade of 12" x 12" timbers may be cut
through by 3 lbs. of gun-cotton to every lineal foot of the required
opening. Slabs are threaded together so as to be in contact, and
hung or laid against the timbers at the level at which it is desired
to make the breach (Pig. 1, PL XLIV,).

To breach a stockade of 10" x 10'' timbers with gunpowder,
40 lbs. placed against the stockade, and covered widi sand bags
filled with earth, are necessary. The cha^ is placed in a coiijSe
of well-tarred sandbags (Fig. 2, PL XLI v.). 60 Iba of powder
placed agwist the same stockade, uncovered, will breach it

A stockade of 14" timbers may be breached by 100 lbs. of
powder uncovered.

For double stockades the charges should be largely increased.

A gate strengthened with iron bars and struts would require,
to breach it, at least 200 lbs. of powder covered with sandbags,
or 80 lbs of gun-cotton.

A 14" brick wall may be breached by 1^ lbs. of gun-cotton, and
an 18" wall by 2 lbs. for every lineal foot, laid against it, or by
charges of 60 lbs. of powder, weighted with sandbags, and placed

5 feet apart.

A wooden bridge may be easily destroyed by exploding gun-
cotton placed in auger holes in the principal supports, or a heap
of combustible materials may be pil^ up in the middle and set
file to ; or petroleum, paraffin, or other omilar combustible may
be poured over the timbera to make them hum.

F. F. H&le^LTf.

HASTY DEMOLITIONS.

^1 I.

« R { I

r li-

•f,n

Ji^.i.

/^.j.

^ecUtm ofDetcnator jSt BidArtG Fi^e.

-GanaiUir^Dim

i jgggtpgjg ^

/■is,,*.

jij,,?.

HASTY DEMOLITIONS. 131

A timber 9 to 10'' square requires about 4 oz. gun-cotton in
auger holes, and one 12'' square requires about 5 oz. similarly
placed to cut it in two.

To demolish masonry bridges, charges are best placed at the Masonry
hauDches or in the.piers (a, Fig. 4, PI. XLIV.) ; but if time pre^js Wdges.
the kejstone may be blown out. (ft. Fig. 4, PL XLIV.) nhen
gim-cotton is used the discs should be evenly distributed across the
bridge, as if placed in a heap, a hole may merely be blown clean
through. Powder should be arranged in two or more charges
unless the bridge is very narrow. The charges should be buried
and tamped.

Iron girder bridges may be destroyed by placing a charge Iron girder
beneath the supports on which one of the girders rests, as at a ^n^ges.
(Fig. 5, PI. XLiI v.). It is better, however, to place a charge at b
and blow down the pier. The hole may be made with jumpers,
boring bars, and sledge hammers, or even pickaxes and crowbars
in the case of brickwork.

40 lbs. of powder in a central position will blow down a small Houses,
dwelling-house.

209. To disable a railway temporarily, remove a rail or two Railways^
(from both up and down lines). The outside rail on a curve is ^ disable,
the beat to select, as it is the most difficult to repair.

When there is not time to disconnect the rails, they may be cut
by exploding gun-cotton against them (Fig. 6, 7, PI. XLIV.); 8 oz.
will cut the heaviest rail.

Bridges across cuttings may be blown down, or the steep sides
of a deep cutting may be thrown in.

To destroy a railway : — To destroy.

Remove the rolling stock ; take up the rails and carry them to
the rear, or throw them into a deep pond or river, or, if there is
time, heat and twist them.

The sleepers and station buildings should be burnt ; the water
tanks rendered useless ; fuel stacks set on fire or removed ; bridges
blown down ; tunnels blown in. It is better to blow in one long
tunnel in several places than several tunnels only in one place.
The charges should be applied at the haunches.

Sails are easily bent by placing them on a pile of burning
sleepers until they become red hot. In this condition they are
also readily twisted by inserting the point of a pick in one of the
bolt holes at either end and bearing in opposite directions.

Telegraphs may be disabled by binding all the wires together Tel€^phs,
with fine wire, first scraping them clean and bright, or removing *^ d«aWe
the instruments.

To destroy a line, cut down the posts, cut the wires, break the To destroy,
insulators, and carry away the instruments.

132

PERMANENT FORTIFICATION.

CHAPTER IV.

PERMANENT FORTIFICATION.

Objects of
permanent
fortification.

Economy of
garrisons.

Resistance to
regular siege.

Durability.

Principles.

Besieger's
operations.

To silence the
fortress.

To approach
under cover.

Section I. — Elements of Permanent Fortification,

210. A definition of peimanent fortification has already been
given, and the nature of the difibrence beween it and field fortifi-
cation has been explained (paragraph 81). In every country
there are some points which, either as sources of supply, or as
giving command of main lines of communication, are sure to be oF
great importance in the event of war. These points can be fortified
in time of peace with a thoroughness that is quite unattainable
when tliey are actually threatened by an enemy ; and the great
defensive strength thus given to them will allow them to be
guarded by a smaller force than would otherwise be necessary, or
by troops of inferior quality. Fortresses, therefore, if properly
placed and properly used, increase the force available to meet the
enemy in the open field.

But the field armies may be temporarily worsteJ, and the enemy
may make great efibrts to get possession of points which have be-
come all the more valuable to him by reason of their fortifications.
These must accordingly be capable of resisting attacks made, not
only by very superior numbers, but during a prolonged time, and
with the assistance of special siege material. In addition to this,
such places may not be attacked for many years after their con-
struction, and they should therefore be fortified in a permanent or
durable manner, masonry and iron being substituted for timber*
work, so that they may suffer as little as possible by the lapse of
time.

21L Notwithstanding the larger means and the larger require-
ments, the main principles of permanent are the same as those of
field fortification : to expose the enemy to the fire of the garrison^
and to cover the garrison from the fire of the enemy ; to put
obstacles in the way of the enemy's entrance, but yet to allow
freedom of issue to the garrison.

212. But in applying these principles regard must be had to
the besieger's methods of attack, and to the advantages and dis-
advantages that belong to him. He will usually first set himself
to overpower the artillery fire of the fortress upon the side whicb
he has determined to attack. He will be free to choose the best
positions for his guns, and will commonly secure great convergence
of fire, and a superiority in the number of pieces ; but the advan-
tage in calibre should be on the side of the defence. Finding no
natural cover, at all events within half a mile of the place, he will
create cover by making trenches, defiladed from the view of the
besieged, along which he may advance close up to the fortress, and

ELEMENTS OF PEBMANSNT FOBTIFICATION. 133

this will occupy him for weeks or months, according to the nature
of the soil^ and the activity and vigour of the defence*

He has then to find means of removing or crossing the special y<^ op^" * 'o<^
obstacles provided to bar his entrance into the place, and this will "^*® *^® P'*"*'
necessarily involve the silencing of any powerful fire flanking such
obstacles. He will do this as far as possible by his distant bat-
teries^ but he may be forced to make new batteries for the pur-
pose within close musket range of the garrison, or to incur the
delays and uncertainties of mine warfare.

Opportune sorties are the most effective means, not only of Offensire
delaying the besieger's progress, but of keeping up the confidence ^l®^**^®^'
of the garrison ; but the scale upon which it may be desirable thus
to assume the oiS^nsive^ and the length to which such counter
attacks should be pushed, will depend upon the proportion of
besieged to besiegers. In ordinary cases, where this proportion Necessary
18 as one to five or more, they must be narrowly limited, and nothing Precautions,
must be done to give facilities for the garrison to come out that
will also make it sensibly easier for the enemy to get in. *

And further, this great inequahty of numbers makes it neces-
sary for the gnrrison, whatever the strength of their works, to be
always alive to the possibility that the besi^ers may cut short the
slow process of a regular siege, and try to enect their entrance by
Budden assault.

213. The two mnin elements of permanent fortifications are a Combinatloii
commanding rampart^ and a well-flanked ditch. The most uni- ^{^i' "*^
versal form in which these are employed is a continuous enceinte,

or enclosure, surrounding the place ; but in the present day it is
usually necessary to construct also a chain of separate enclosed
works, or detached forts, at some distance from the body of the
fortresjs, and these works may to some extent supersede the
enceinte as the main line of defence, and reduce it to a mere
provision against assault or surprise.

The Rampart and Parapet

214. The rampart (Fig. 1, PI. I.) is the bank, formed chiefly of Rampart,
the earth excavated from the ditch, upon which the parapet stands.

It adds to the height to be climbed by an enemy in an
assault, hides the interior of the place from the besieger^s view,
and, above all, affords a commanding position for fire upon the
ground in fi'ont. Such command is valuable, because it aggravates
the besieger's difficulties in making his nearer approaches, and it
is necessary where, as is often the case, there are outworks beyond
the ditch, over which the main work must fire. The crest of the
latter, therefore, is usually from 20 to 30 feet above the natural
.ground.

The thickness of the parapet must not be less than 24 feet, to Parapet.
bear the fire of heavy siege guns and the large bursting charges of
their shells ; but on fronts not likely to be exposed to continuous

134

PEBMANENT FOBTIFIOATION.

Banquette.

Terreplein of
the rampart

Interior slope.
Kamps.

Dispositions
for the service
of artillery.

Trace of
ramparts.

Artillery
carriages.

firing 18 feet is enough. The penetration of such shells into
compact earth is seldom more than 12 feet, but this is nearly
doubled when the earth has become loosened by successiye explo-
sions. Sand is the best^ and clay the worst, kind of earth for
resisting penetration.

The superior slope should not be steeper than ^^ and if possible
only ^. The exterior slope should seldom be so steep as ^,
usually only -^ ; and when it is long a S-feet berm should be left at
about every 12 feet of height, and a quickset hedge planted upon
it. Such hedges help to maintain the slope under fire, and are
also obstacles to assault.

The banquette is formed as in field works, but during peace
time the interior slope is left unrevetted at ^, and so covers two
thirds of the tread. Steps of masonry or wood are sometimes
used, and occasionally it may be found desirable to provide either
corbels or short transverse walls, to receive planks as temporary
banquettes when required.

The 'terreplein, or upper surface of the rampart behind the
parapet, is about 8 feet below the crest. To give room for work-
ing the guns and for a road in rear of them it has been usual to
make it about 40 feet wide from the crest to the inner edge. But
in new works the roadway is now commonly sunk to about 12'
below the crest, so as to obtain cover from shots at the ordinaiy
angles of descent of direct fire(scil. 8^ or less), and separate ramps
are made from the roadway to the gun terrepleins. This makes
it necessary to increase the entire width to about 60 feet. (Fig. 1,
PI. I.)

The interior slope of the rampart is usually made at 4^, unless
there is some special reason for building a retaining wall.

Wide and easy ramps must be made up the interior slope at the
most convenient points, to allow of the ready movement of guns
from place to place. They should be 10 or 12 feet wide, and
from ^ to 3^ in inclination, according to the height of the slope.
The short ramps from the roadway to the gun terrepleins need
not be more than 8 feet wide, and may be made steeper.

215. The rate of progress of siege depends chiefly upon the
extent to which the fire of the garrison, more especially the artillery
fire, can be kept under. It is of the first importance, therefore,
for a vigorous and prolonged defence that the ramparts should be
so organised as to give the utmost security to the guns and gun-
ners, and the utmost effectiveness to their fire.

They should be traced, so far as other considerations may-
allow, with obtuse salients, and without re-entering angles, so
that they may give a strong frontal fire upon the capitals, and may
be less easily enfiladed.

With the ordinary service carriages the guns on the ramparts
can only fire over a height of from 2 ft. 6 in. to 5 ft., according to
the mode in which they are mounted and their angle of elevation.
They must therefore, in any case, either be placed on gun-banks^
or be provided with embraj:ures.

ELEBCBNT8 OF PEBICAKBNT FOBTIPICATIOIT. 135

\ The lieight of the axis of the tnumioiiB is as ibilows :—

ft. in.
Field guns on field carriages - - about 3 6

40-pr8. or 64-prs. on standing ^rrison carriage „ 3 3
„ ,, on siege carriages - - „ 4 5

64-pr8.^ or 7-inch guns on sliding carriages on

awarf trayersing platforms - - ,,6 8

The height of parapet, therefore, for direct fire at short ranges^
may be taken as 3 ft. for field guns, and 2 ft. 6 in., 3 ft. 6 in.,
or 4 ft. 3 in., according to the carriage, for heavy guns.

On gun-banks allowing of fire over the parapet, the guns and Barbette fire.
gun detachments are very much exposed. They are suitable,
therefore, only for field guns^ which can be quickly run up and
down^ and can be shifted from place to place before the besieger
brings his fire to bear on them. Such pieces are very useiul,
especially in salients where they can command a wider field, to
sweep the immediate foreground iu case of an assault, and to
delay the besieger's advance by firing from time to time upon the
heads of the approaches (e.ff., Fort Bellevue, Belfort). As already
stated la. the chapter on Field Fortification (par. 118), the width
from the base of the interior slope to the rear edge of the gun-
bank should not be less than 20 ft., and 15 ft. of crest line should
be allowed for each gun. fionnettes may be made on the parapet
at Intervals, which will give some protection to the guns against
oblique fire (a. Fig. 2, PI. I.).

Embrasures allow of better cover, especially against musketry, Embrasureg.
but their defects, which have been already pointed out (par. 1 18),
in relation to field works, become even more serious where heavier
guns are concerned.

Deep embrasures, therefore, should never be used except where Deep,
they are sheltered from direct fire, and have only to command a
small field, as in the fianking of ditches. Even here they should
not be more than 4 ft. deep, (ft. Fig. 3, PI. I.)

Where they are exposed to direct fire their depth should not Shallow,
exceed 2 ft. 6 in. ; they should be about 4 ft. wide at the throat,
and their cheeks inclined at \ throughout. If they are them-
selves intended for direct fire at short ranges, it will be necessary
to raise the terreplein behind them to within 6 ft. or 6 ft. 6 in. of
the crest, and to carry the embrasures through to the exterior
slope (c, Figs. 2 and 3, PI. I.). For indirect or high-angle fire,
the terreplein need not be raised if the guns are on traversing
platforms, and the soles of the embrasures may be made counter-
sloping (rf. Fig. 2, PL I.).

The intervals between embrasures must be 1 8 ft. from centre
to centre, to give room for the working of the guns, and they
ought in most cases to be considerably more, in order that the
parapet may not be too seriously weakened by them.

216. The great inconveniences attaching both to ordinary bar-,
bette fire and to embrasures, which have become much more serious
since the introduction of rifled weapons, make it very important
to find some means of escape from them.

136

PERMANENT FORTIFIOATION.

Monerieff
carriage.

Haxo case-
mates.

Iron shield
and turrets.

Mortar case-
mates.

Traverses.

One such means is offered by the Monerieff carriage.. This
allows a 7-inch gun, after being fired en barbette^ to recoil for
reloading into a sunken emplacement, or pit, the floor of which
is 10ft. or lift below the crest (e, Fig. 3, PI. I.). Except at
the moment of firing, therefore, the gun is completely protected
against direct fire ; it remains exposed, however, to curved and
high-angle fire.

To give protection against these, guns are often placed in gun-
rooms of masonry with bomb-proof arches, which are known as
Haxo casemates* (Fig. 1* PL II.)*

The front wall of these casemates is covered as far as
possible by the earthen parapet, bonnettes being made for this
purpose upon the merlons. Still, at the embrasures tlie masonry
of the front wall and arch is unavoidably exposed, and it would
be necessary therefore now to cover this portion with iron where-
ever it is likely to be subjected to continuous direct fire.

Iron shields, of the kind adopted in earthen batteries against
shipping (see Coast Defences), may occasionally be made use of; or
guns at salients may be mounted in revolving iron turrets. Such
protection will allow the defender to turn to fullest account the
advantage which belongs to him of employing larger calibres than
the besieger is able to transport, for ordinary siege guns will make
little impression on 10 inches, or 12 inches, of iron. But owing to
its great cost, iron plating has hitherto been, and will probably con- •
tinue to be, very sparingly applied, and only for the heavier. guns.
The bulk of the armament must always remain dependent on
earth cover.

Casemates for mortars are also sometimes made on the rampart.
They correspond generally to the gun casemates (Fig. 1), but tlte
front wall is omitted and the casemate is set back four or five yards
from the parapet, and is sunk so as to be completely masked by
it, the interior slope of the parapet being formed at -^. Mortar
casemates, however, are more often placed under the rampart, so
as not to occupy space that might be used for guns, or they may
be placed behind the rampart in the interior of the work. It is
of less importance that they should be built beforehand, as they
can be improvised without much difficulty in the course of a
siege, wherever they may be wanted.

217. Traverses must be provided, even upon faces that are not
exposed to enfilade, to give protection against oblique fire, and
against the splinters of shells. To intercept descending shots it
is desirable that they should be high, but «on the other hand tra-
verses that stand up above the crest line have the disadvantage of
indicating to the enemy the probable position of the guns. If
they are not made more than 3 ft. higher than the crest, this in-
convenience may, perhaps, be avoided by planting a hedge of broom

* The term casemate, probably from the Spanish casa matar (house for killmg)^
was originally applied to what would now be called caponiers, but it has been
extended to yaulted chambers in general, eyen when used merely as quarters.

Fig, I, StvUoti t^ Bianpurt f-'ieale j&ij

^^k---^

(•Snde -,-M )

u^irt

Sear ElevecUan..

ELEMENTS OF PEBMANENT FORTIFICATIOX. 137

as a screen upon the parapet, a few feet from the exterior crest.*
On faces directly enfiladed^ concealment is less worth studying,
and the traverses may be carried up 6 ft. or more above the crest^
to give better cover against curved fire, (Figs. 2 and 3, PI. I.)

Their breadth will vary according to the fire they have to resist,
and according as they are solid or hollow. Splinter-proof tra-
verses {ff^ Fig. 2)9 may be only 6 ft. broad, being built up with
two rows of gabions (v. Siege Works). Others will be from
15 ft to 30 ft. at the level of the crest line of the parapet, with
side slopes usually of \y which can be cut away and revetted, if
required, on the sides not exposed to fire.

Their ordinary length ii» from 24 ft. to 30 ft. behind the crest
They may be carried forward on to the superior slope to guard
against oblique fire. It may be necessary to prolong them to the
rear, where the parapet might otherwise be taken obliquely in
reverse.

Against fire directly in reverse parados must be employed Fftndos.
(Fig. 3). These, however, have the great disadvantage that
they arrest shells that have passed over the parapet in front of
them, and the splinters fly back upon the men on the terre-
plein. They should, therefore, be no higher than is absolutely
necessary.

The intervals between the main traverses maybe from 12 to 24 Intenmls.
yards on faces that are not likely to be enfiladed, allowing room
for two or three guns ; but on faces exposed to enfilade it is better
to reduce them to about 9 yards or less, and to have ordinarily
only one gun in each interval.

218. Some or all of the traverses are made hollow, so as to Shelters.
afiTord shelter to men, guns, and ammunition.

There are casemates, usually under the ramparts (Fig. 8, PL III., For men.
and Fig. 2, PI. XV.), for the part of the garrison that is off duty,
but of the men required upon the ramparts, there are many who
need nofc remain exposed to the besieger's shells, provided that
ihej are ready at hand when wanted. Infantry guards and field-
gun detachments kept in readiness against an assault, bearers to
carry off the wounded, and spare men to tak« their places, should
all be under cover, and Avith deliberate firing the gunners em-
ployed may also seek shelter from time to time.

Field guns until they are wanted, may be in the shelters them- For guns,
selves, or just outside of them, well covered by the traverses.

The shell stores and powder magazines are usually below, under For ammoni-
the ramparts, but lifts from them may be carried up into the shel- ***'°' .
ters for the secure supply of ammunition, and cartridge 'Stores may
be made there, to hold a few rounds for the immediate service of
the guns. These may even become expense magazinesy capable of
containing a 24-hour8' supply, in positions where it might be
difiScult to replenish them.

* Experiments have shown that a screen of this kind does not cause the explosion
of shells with percussion fusses, and gaps for aiming can easily be made in it.
(Brialmont: Fortification a Fosses Sees.)*

42642. K

138

PfiRMAKENT FORTIFICATION.

shelters.

Ammimttion recesses may be made under the parapet, or under
hcmnettes (Fig. 5, PL IL), to contain a few rounds in readiness for
an assault.
Gonstractioii of FigB. 2, 3, and 4, PI. 11. , give some examples of hollow traverses,

oorresponding to those shown in Figs. 2 and 3, PL I.

The entrance will be made at the side or end of the traverse,
according to whichever ma; be least exposed.

To be proof against the shells of heavy siege guns the arches of
the shelters should be 3 feet thick, and should be covered by 5 feet
or 6 feet of earth ; and there should not be less than 10 feet of
earth protecting the side walls. The roof may be formed of con-
crete and iron girders (Fig. 4), instead of brickwork, wherever
arches are inconvenient.

The following facts were noted during the defence of Paris in

1870-1 :— *

A hollow traverse with a 2 feet arch and 5 feet of earth cover
was pierced by a 60-pr. shell.

Similar traverses covered with 8 feet of earth, though often
struck, were never pierced ; but in some cases the arch w^ injured
by the explosion of the shdls.

Arches 3 feet 3 inches thick were pierced when covered by only
3 feet of earth, but not when covered by 6 feet.

The Ditch.

i^jtch. 219. The ditch in front of the rampart may be wet or dry : this

will generally depend upon the site. In the one case the obstacle
is formed by the water, in the other by the escarp and counter-
scarp.

Wet ditches. 220. Wet ditches, therefore, should be broad, as the difficulties

experienced by a besieger in effecting a passage across them will
increase with the length of bridge which he will have to construct.
. On the other hand, as the bridge made may be a floating bridge
(e,ff. Strasbourg, 1870), it is not worth while to make wet ditches
deep, especially as excavation below the natural water level is
difficult and costly. The usual depth is from 6 feet to 10 feet
below the surface of the water ; the width may (as at Antwerp)
be nearly 100 yards, though it is usually much less than this.

The escarp and counterscarp are seldom revetted^ but are
formed at a slope of ^. A wide berm is left between the base
of the rampart and the top of the escarp, and a hedge may be
planted on it. Occasionally a wall is made, for the water obstacle
is not in itself a con^plete security against surprise, and in winter
it may be frozen over.

Diiidvantages. Wet ditches have the disadvantage of rendering the conununi-

catioDS with the outworks difficult and insecure during a siege,
and tending, therefore, to confine the garrison to a* passive
defence.

Also^ if the water is stagnant, it is injurious to the health of the
garrison. There should always, therefore, if possible, be some

♦ See Reviie d'A'rtillerie, January 1874.

Fi0. J. H(tav Oisematc.

P. F.

Fig. 2. FhAiow Traverse.

^b.v

j<«r«

I.:

Ir-

Front ELevoUiori.

Ftq. S, HoUow Thayense, to sh4*lter field guns.

Shells T

J t

LJ-:-

Y^-

Serficn on A3.

*2fi

Fig. 6. fSfu'll Recess underBoruietU

». I...

/V^jr. /' . Hollow Trcwerse.

*-l9

f 6 ■

•MfcMMte

*■'■'■ i.1-- ./

r+H3.

♦ 33

tnTTilliiiirvifi I i

v,*l>

Section on C D.

-v.^

+ 25

+ 19

l.t^

A 22 3

L^''

Section on E F.

(Scale 360.)

Opp. tppaxfi' /38

":cll Liih 2Z Bedford 3'- Zcxzv.: "aii^r.

BLEMfiNTB OF PERMANENT POBTIFIOATION. 139

current ; and if the current is strong it will add considerably to
the difficnlties of the besieger's passage.

These will be further increased if the garrison haye sufficient Water
command of water to be able to fill or empty the ditch at pleasure. »«»•«▼»••
For water matuEuvres of this kind^ dams or batardeaux with sluices
will be required, to regulate the supply. They must be well pro-
tected against curved fire, so that they may not be breached by
the besieger ; and they must be so placed and shaped as not to
furnish a bridge for him across the ditch.

221. With dry ditches the escarp forms the main obstacle, and Thy ditches,
this is ordinarily a wall, either acting as a retainint;^ or revetment ^
toaU to the rampart, or standing as a detached wall in front of it.
When the natural soil is rocky it may be sufficient to scarp it.

The main requirement here is that this wall should be high '^*^**P '^^^^
enough to give security against assault, and that the top of it
should be suuk so low that the besieger will not be able to breach
it from a distance.

The necessary height of wall used to be reckoned as at least ^^^t..
30 feet, but the difficulty aud risk attending an attempt to esca-
lade have been so much increased by the introduction of rifled
arms and breechloaders, that about 15 feet is now sometimes
thought sufficient. It should at all events be such as to compel
the enemy to bring up ladders.

The top of the wall should be screened not only against direct ®^"*° *°8^^-
fire^ but also if possible against curved fire having an angle of
descent of i (14°).

In the course of the breaching experiments at Fort Li^ot, in
the Isle of Aix, in 1863, a practicable breach was made in an unseen
reyetment by a battery three quarters of a mile distant, firing with
an elevation of 10^, or an an^j^le of descent of 12°* If the Ime of
fire is at 60^, horizontally, to the line of wall, an angle of descent
of 12° becomes equivalent to an angle of 14° on a line of fire per-
pendicular to the wall, for the shot strikes equally low after grazing
the screen in front, supposing that to be parallel to the wall.

When the wall is screened to tliis extent it is not only difficult
for the besieger to breach it by curved fire from a distance, but it
is also difficult for him to breach it by direct fire from batteries
on the counterscarp.

Even if the necessary depression can be given to the guns, the
men serving them will be greatly exposed to the fire from the
ramparts.

But this condition is not always easy to satisfy, and it is far m-protected
from being satisfied in all except the most recent fortresses ; for **'^'
before the time of rifled artillery it was thought almost sufficient
that the escarp should be hidden from view. And although it
will seldom be wise to build walls which can be breached from a
distance, and need not, therefore, delay the besieger's progress,
yet it is necessary to remember that where such walls are already
built, they have b^ no means become valueless. To form a prac-

♦ Brialmont: l^'ortificatioo a Fosses Sees, i. 150.

K 2

140

PKRMANRNT PORTIFICATIOK.

Glacis.

Width of the
ditch.

Counterscarp.

Revetmont
walls.

ticable breach they muBt be destroyed for more than half their
height, which, if not impossible by indirect fire, may require a very
large expenditure of ammunition; and after all, the portiona
breached will form a very small part of the entire line of wall,
offering only narrow and difficult defiles to the storming columns.

The screening of the escarp wall is assisted by the glacis, which
is always formed on the outer side oF the ditch, and is sometimes
brought up to the counterscarp. For instance, if the glacis id
8 feet high, with an interior slope of \, and the ditch is 40 feet
wide, a wall 16 feet high will be sufficiently hidden when the
ditch is made 20 feet deep. (Fig. 2, PL IV.) But a depth of
25 feet or 30 feet may be necessary when the crest of the glacis
is more distant, or tlie wall higher. (Figs. 4, 5.)

Deep ditches add something to the besieger's difficulties in
crossing them ; but on the other luind, the cost of the excavations,
and the length or steepness of the ramps leading into them, are in
proportion to the depth.

222. It is plain that the escarp will be most easily screened
when the ditch is narrow. The width of main ditches used to be
from 20 to 30 yards, but this is now commonly reduced to 15
yards ; and for secondary works 10 yards or 8 yards may suffice.
Less than this might allow an enemy to pass by fiying bridges ;
an I, in any case, to narrow the ditch is to diminish the amount of
flank fire which can be poured into it, and to make it more pos«
sible for the besieger to forip a dam across it by exploding largj
mines behind the counterscarp.

223. The counterscarp is usually revetted, at all events for 15 ft.
or more of its height. It thus presents an additional obstacle to
an assault, of less value than the ei-carp, but less easily destroyed.
Also it lessens the distance between the escarp -and the crest of
the glacis, so that the former is better covered. For economy,
however, it is. sometimes left as an earthen slope at ^, to be pro-
vided with some of the accessory obstacles used in field fortification
when the place is prepared for defence.

Occasionally portions are made at a' slope of ^ or J (^lacii en
contrepente), to allow the garrison, in making sorties, to issue on a
broad front from the ditch.

224. Besides the main distinction, already mentioned, of revet-
ment walls and detached walls, there are several minor distinctions
according to construction.

If a revetment wall is carried up to the level of the terreplein
of the rampart it is called sl full revetment ; if it stops short of
this, a demi-revetment (Figs. 1 and 2, PI. III.).

Where there is a full revetment, a masonry wall usually, but not
always, takes the place of the exterior slope of the parapet (Fig. 1,
PI. ill.). Full revetments are common in^ old fortresses, but tbejr
are never adopted now in fronts exposed to artillery fire, as it ia
impossible to cover them from the enemy's view. Owing to the
absence of the exterior slope, they afford more interior space, which
for small works is sometimes of importance. They also offer a

ELEMENTS OF PBBVAKENT FOBTIFICATION. 141

better obstacle to escalade than demi*revetinent« do» suppoting the
relief to be the eame in each caae, not only because of tneir greater
height^ but because the assailants are exposed to the defenders'
fire at the moment of reaching the top of tne waU. On the other
hand, if breached at any given height below the crest, much more
of the parapet falls with a full, than with a demi^reretment {see the
dotted lines on Figs, 1 and 2).

Eevetment walls are further distinguished, according to their
profile, as rectangular^ leaning^ sloping^ and countersloping (Figs. 2,
3, I3 and 4, PI. III). The first is an upright wall of equal thick-
ness throughout ; the second is inclined towards the bank, sup-
ported; in the third the base has a greater thickness than the
top^ the back is vertical, and the face of the wall has a slope.
The fourth is the reverse of the third, the face is vertical, and the
back is inclined. In this case the back is often built in offsets
(Fig. 6) instead of in one plane.

In comparing the stability of these forms it must be assumed
that the cohesion of the materials of the wall, and the friction of
the ground underneath, are such, that the wall, if it gives way, will
turn over bodily on the outer edse of its base. So compared, the
theoretical stability of a rectangular revetment being 1, that of a
leaning, a sloping, and a countersloping revetment will be about 2,
2i, and 1 respectively, the slopes in all cases being taken as f .
This comparison, however, deals simply with the walls themselves,
and leaves out of account the influence of the earth behind them.
The downward pressure of this upon the back of the countersloping
revetment adds very much to its stability. A countersloping revet-
ment has also the advantage that, the joints on the face being
horizontal, the rain-water does not find its wav into the heart of
the wall, as it does along the inclined joints of the fiftces of sloping
or leaning walls, when made of brick. Consequently it is more
easily kept in repair, and is the form that is now usually adopted.
But as, with a perfectly vertical face, the least yieldms of the
foundations will make it overhang, and it will be brought away
readily in breaching, a slight 3lope, or batter, is offcen given to it
in addition to the counterslope.

225. The stability of a retaining wall Is much increased, and the Counteiforts.
mass of it may consequently be much reduced, by placing
buttresses at intervals; but as any projections are inadmissible
upon the face of escarp and counterscarp walls, counterforts are
here employed instead. These are built at the back of the wall
and act as ties, while buttresses would act as struts. They add
to the natural stability of the wall, not only by their weight, but
also by the friction of the earth backing against their sides.

Counterforts are termed, according to their plan, rectangular,
^dovetailed, and diminished. In the first case the sides are parallel ;
in the second the width at the tail, or part furthest from the wall,
is greater than at the root, so as to throw the centre of gravity
further back, and obtain a stronger hold on the mass of earth ;
in the third the root is wider than the tail, so as to strengthen the
bond between the wall and the counterfort. The rectangular
form is that most freqxiently employed, and is of simplest con-
struction.

226. The following proportions were assigned for counter- Pasley's
>ping revetmc • - ^ -- .

experiments:^ —

sloping revetments by General Pasley after a long course .of ^ountersteping

-° revetiQeats*

142

PBBMAKENT FOSTIFIOATIOK.

Counterarched
reTetments.

Adyantages.

Construction.

Sosketiy
^allenes, aud
gun rooms.

Countenlopey in all caaes - • ' i , .

CountefBcarp reretmenta, mean thickness - ^ their height.
Full revetments - - - - ^

Demi-revetments, with berms of one fourth

their height - - - - - H

Demi-revetmenta» with narrow or no berma - ^
Counterforts, rectangular, with counterslope of f , —

Length - - - - - \ their height.

Thickness, 2 ft. 6 in. for a wall 10 ft;, high, and 1^ in.
added for eveiy additional foot of height.

Distance from centre to centre, four times their thickness.

227. Besides solid revetments^ which have hitherto been chiefly
in view, there are also hollow or counterarched revetments (Figs. 5
and 7, PL III.). It is one great advantage of counterforts, that
they lender the formation of a breach more difficult, by retaining
the earth between them at too steep a slope to be accessible, after
the front wall has given way. This advantage may be increased
by prolonging the counterforts, and turning arches between them,
which serve to support the earth above, and to relieve the front
wall from all, or nearly all, pressure. The thickness of this front
wall, therefore, may be very much reduced, and its destruction
will not involve the fall of the parapet, or open a practicable
breach. It will still be necessary for the besieger to bring down
the arches by cutting away their piers, a long operation in any
case, and especially difficult by indirect fire from distant batteries.

Also, as an increase of height will not increase the quantity of
masonry in a counterarched revetment in so great a ratio as in a
solid revetment, it becomes a more economical form of construe-
tion in the case of high revetmentf>. On this account it is often
adopted, not only for escarps but for counterscarps.

It has, too, the further recommendation that it provides useful
bomb-proof cover, if required, and that if the front wall is loop-
holed it may furnish a valuable fire in the last stage of a siege.

The arches may be in one or more tiers, according to the height
of the wall ; but the upper arches should be kept at least 3 feet
below the top of the wall, so that they may have earth enough
above to protect them. For ordinary spans, about 12 feet,
a thickness of 1 foot 6 inches with a rise of 3 feet will be suffi^-
cient for them. The counterforts are commonly from 9 feet
to 15 feet long, and about 4 feet thick, the front wall from 3 feet
to 4 feet 6 inches thick. If no gallery is required, the earth
may be allowed to enter from behind, under the arches, at its
natural slope (Fig. 6). If the revetment is to be made use of
for a gallery back walls must be built, and it is best to curve
these on plan (Fig. 9) to resist the pressure of the earth. Passage
ways, 3 feet wide, must be made through the counterforts.
Loopholes may be pierced in the front wall about 4 feet apart,
and above them, immediately under the crown of the arch, an
outlet for smoke should be made.

Loopholed galleries, whether escarp or counterscarp, will in
some positions furnish fire, not merely across but along the ditch,
and become therefore pf great importance for its flank defence,

ELEMENTS OF PBEMANSNT FOBTIFICATION. 143

In BQch posidoiiB artillery ma^ be required^ and the bays of the
gallery may be lengthened into gun-rooms. Or, as shown in
Fig. 8, the men's casemates under the rampart may be carried
through to the escarp to furnish artillery or musketry fire.

Although counterscarp galleries are often most useful, not Coontenoarp
only for fire upon the ditch, but also as a base for countermining, revctmenu.
they have the drawback that they are serviceable to the besieger
when he has succeeded in working into them (e,g. Strasbourg).
It is better, therefore, where there is no special need for them,
to revet the counterscarp with piers and arches only, without any
firont wall (Fig. 3, PL IV.), unless a thin wall is required to prevent
the enemy getting shelter in the recesses thus formed.

228. Detached walls are sometimes made (as in Fig. 5, PI. IV.) Detached
about 7 feet thick, with arched recesses, and loopholes, so as to ^^*
furnish a line of fire, and to protect the men posted there from
enfilade. The loopholes must be more than 6 feet above the
bottom of the ditch, so that they cannot be used by the enemy,

and the ground behind the wall must therefore be raised. But
if the wall is sunk low, the field oC its fire wiU usually be very
limited, and men placed behind it will suffer from the splinters
of shells that burst in the exterior slope. It will probably be
worth while to man it only where it gives a flanking fire. Else-
where therefore it is cheaper, and is now more common, to build
a solid wall without loopholes about 3 feet thick, which can be
flanked in rear as well as in front (Fig. 2).

Besides costing less than revetments, detached walls offer a Adyantages.
better obstacle to escalade, since the enemy have to descend as
well as to mount the waU. They are more easily breached if they
can be hit ; but on the other hand, the breach made is rougher
and less practicable, and the exterior slope of the parapet remains
standing, presenting fresh obstacles in the hedges on its berms.
A breach in a revetment necessarily confines the assailants to the
narrow defile which it offers ; but with a detached wall there is
some danger that the enemy, penetrating at one point, may then
spread right and left, and mount the rampart on a broad front.
To hinder this, transverse walls with loopholes may be made at
intervals, running back from the main wall into the exterior
slope ; or instead of these walls, palisades or iron railings may be
used, which will not interfere with the fire of the flanking works.

The great length of the exterior slope, and the consequent Disidxaatagci.
breadth of the interval between the escarp and the crest, where
a detached wall is adopted, sometimes preseiits inconveniences.
It makes a higher command necessary, diminishes the interior
space, and to some extent interferes with flank defence from the
parapet. On these accounts a revetment wall may often be
preferable.

229. A comproiiiise between the two, which is sometimes Bevetment j
better than either, is offered by the semi-detached wall, or re- T**^ ^^f^^^
vetment with chenan des rondes (Fig. 4). Here the revetment ^ ^°° ^^*

144

PERMANENT FOBTIPICATIOK.

Bottom of the
ditch.

stops about 7 feet below the top of the wall ; there is a berm
3 or 4 ynrds wide, the inner part of which serves for the patrol
path, while on the outer part the wall is carried up as a detached
wall, with a thickness usually of 3 feet. This 3-feet wall may
be loopholed, or a banquette with steps may be made to allow
men to mount and fire over it. The destruction of the upper half
of the escarp in this case would leave the parapet almost uninjured,
and the patrol path gives facilities for repairing any damage done
to the exterior slope, as well as for keeping a good look-out
against surprise, and offering an energetic resistance to escalade.

230. The bottom of the ditch slopes downward from the
escarp and counterscarp towards the middle, and a drain is made
there to carry off the rain water. This slope is usually very
slight, but it may sometimes be considerable on the counterscarp
side, to save the expense of an unnecessarily high wall (Fig. 4).
The drain is occasionally enlarged into a cunette^ about 6 yards
wide and 6 feet deep (Fig. 1, PI. III.), forming a small wet ditch,
and presenting an additional obstacle to the besieger, alike in an
assault, and in the attempt to carry his trenches across the ditch.
Ounettes are especially useful in wet ditches in which the
general depth of water would allow of fording.

The covered
way.

Modifications^

sometimes

necessary*.

The Covered Way and Glacis.

231. If no cover for the defenders existed beyond the counter-
scarp, they would not only have great diflSculty in making sorties
In force, but could not with safety even post a sentry on the
further side of the ditch. With an enemy in their neighbourhood
they would, therefore, be at all times liable to surprise. To
obviate this, a space is commonly left between the glacis and the
edge of the' ditch, which is called the covered way. The glacis
forms its parapet, and it is provided Avith a banquette formusketrv
defence. A breadth of about 11 yards has been usually given
to it, so that it affords a roadway 20 feet wide in which a laro-e
number of men can bo assembled (Fig. 4, PI. IV.). It enables the
garrison, when the besiegers arrive near the place, to oppose
them with a close fire of musketry, and to attack them at any
hour of the day or night. This obliges them to keep a large
force constantly at hand, which being confined in a small space
necessarily suffers much from the high-angle fire of the fortress.

Parts of it are often palisaded before a siege to prevent a rush
of the enemy into it. The pali.-atles are placed either at the base
of the interior slope, or about 2 feet inside of the slope of the
banquette, their points rising little, if at all, above the crest.

The covered way, by widening the interval between the glacis
and the escarp, makes it more difficult to screen the latter from
indirect fire. In fact >Yith the ordinary height of the glacis,
8 feet, it will intercept no &hots descending at \ that would not
also be intercepted by the eounterscarp* It will often be better.

ELEMENTS OF PERMANENT FOBTIFTCATION. 145

therefore^ while heightening the glacie to narrow the covered way.
Except where troopa are to be assembled fur sorties, it may be
reduced to a mere patrol path (Fig. 3), 6 feet wide and 7 feet
belowkthe crest Niches can be made in the interior slope of the
glacis for sentries and sharpshooters. In the fronts of small
detached works it may often be dispensed with altogether, as
troops can issue at the gorge and move round by the flanks ; and
even where a wide covered way is necessary it may be best to
brinsT the glacis right up to the counterscarp, and to place the
covered way at some distance to the front, covered by an
advanced glacis. In such a case the exterior slope of the inner
glacis will be prolonged below the natural level of the ground to
obtain earth for the advanced glacis.

The exterior slope of the glacis may ordinarily vary from J to Exterior slope
^V- If steeper than J, it could hardly be swept by the fire oi of ihef^^A.
the rampart behind it; if flatter than -^^ it will require too
much earth for its formation. For this latter reason the height
of its crest can seldom exceed 12 feet, and will usually be nearer
8 feet.

Occasionalljr it will not be possible for outworks to sweep their
own glacis without being given an inconveniently high command.
In such cases it may be better to rely on flank or reverse fire
from other works, and the limit of steepness will no longer apply.
With irregolar ground it may be necessary to scarp the more
advanced part of the glacis^ at something under -^^ forming a '
glacis coup^.

The Profile.

232. From the foregoing it will have been seen that in Conditions
determining the form of the profile to be adopted for any ^^^^^ ^
permanent work, it is important to fulfil the three following ^ument iro^.
couditions : —

(1.) The escarp wall should be covered by the glacis, so as

not to be breached from a distance :
(2.) The musketry fire from the rampart should defend the

glacis and the covered way, up to the edge of the

counterscarp :
(3.) The glacis should also be swept throughout by artillery

fire.

These conditions have to be reconciled as far as possible with
the limits of command, and of width and depth of ditch, the form
of escarp and of covered way, which it may seem desirable to
adopt. It is not necessary, as in field fortification, to balance
strictly the excavation and filling upon the profile, for in
permanent works the earth can be removed to considerable
distances, and the balance when made must take account of the
trace, and of modifications of the ground that may be required
beyond the glacis and inside the place.

If the glacis is to be defended by a grazing fire of artillery, it
will be sufficient that the plane of its surf.ice shjul 1 pass 3 feet
below the crest of the parapet, even if the guns fire through

146 PBRMANENT FOBTIFIOATION.

embrasures. Instead of this it may sometimes be necessary to
reckon on barbette fire> and to be satisfied if this, after gradng
the crest of the glacis, passes not more than 4 feet above the foot
of the glacis. On the other hand, it has been often thonght
desirable that the soles of the embrasures should be so formed
that the artillery fire must pass 3^ feet above the crest of the
glacis, so that infantry who may be on the banquette of the
covered way may not be injured by it.* To fulfil this, the plane
of the glacis must pass at least 6^ feet below the crest of the
parapet. In proportion as it passes lower than this, the artillery
fire will become more plunging.

> For the complete defence of the covered way by musketry, the
plane of the superior slope must not pass more than 4 feet above
the edge of the counterscarp.

Hence it is evident that the command is closely connected with
the slope of the glacis, and with the distance from crest to crest.
The steeper and more distant the glacis is, the higher must be
the main work to defend its slope. The narrower the ditch or
the exterior slope of the rampart, the lower must be the main
work to defend the edge of the counterscarp.

Construction 233. To take an example. Suppose the dimensions of the
of the profile, glacis and covered way to be fixed: the exterior slope of the

glacis to be -g^, the covered way to be 33 feet wide, and 8 feet
below the crest of the glacis, with a fall of 6 inches to the rear
for drainage, so that the edge of the counterscarp is 8 ft. 6 in.
below the crest (Fig. 4, PI. IV.). If a line, ah^ be drawn parallel
to "the glacis and 3 feet above it, then if the crest is in or above
this line, its command will be sufficient to admit of a grazing fire
of artillery from the rampart. So if a line, dc, be drawn from a
point c, 4 feet above the edge of the counterscarp, and inclined
at ^ (supposing tha« to be the intended superior slope), then if
the crest is in or below this line the covered way will be properly
defended.

These lines, a b and d c, intersect at ^, and consequently e is the
position which would give the minimum command for the crest,
while satisfying these two conditions. But they would equally
be satisfied by any point lying between de and ae, and other
conditions may make it necessary to place the crest higher and
further back. For instance, the width of the ditch may be fixed
at 50 ft. In that case, the enemy's fire descending at ^, will strike

the escarp more than 20 feet (viz. * — "^ — ) below the crest of

the glacis. To screen a high escarp com[>letely it would be

♦ Vauban wished to apply he same principle to musketry fire. " Speaking of the
*< defence of Mayence, during which many soldiers had been killed or wounded in
** the covered way by their comrades firing from the rampart above, he said, ' If
'' ' I had my way, I would always direct the superior slope on the points of the
<< * palisades of Uie covered way.'" (Brialmont: Fortification a Foss^ tiecs, i.
273.)

ff 99

»» »f

ELEME^S OF PBKMAKENT FOBTIFIOATION. 147

neeess^ry to have a very deep ditch, and it may be decided,
therefore, to adopt a revetment with chemin des rondes, so that if
the upper part is breached, the parapet behind will be unimpaired.
Then, if from the point ^, the inner edge of the chemins des rondes,
a line gf be drawn equal and parallel to the intended superior
slope, and from y a line Jf^, parallel to the exterior slope, the crest
must be somewhere in the portion of this line lying between d e
and ae. If it is placed at/' on de, it will allow of a sliorhtly
plunging fire upon the glacis, which adds to the besieger's difficulty
in establishing himself there.

The height thus obtained for the crett is easily calculated ; for
if x»the command over the crest of the glacis^

X -|- 8*5 a* the command over the top of the counterscarp,

and
6 (« -f 8*5 — 4) » the distance from the counterscarp to the crest

of the parapet,
r 50 ft. (width of ditch).
+3 ft. ^thickness of wall).
=•< -f 6 ft. (width of chemin des rondes).

+20 ft. -f « — 4ft. (width of exterior slope).
L-f 24 ft. (width of superior slope).
» 99 ft. -f a? (assuming the dimensions shown
in Fig. 4)
or a? « 14'4 feet.

If^ on the other hand, the minimum command were taken (sail,
the point of intersection of j^ with a e), this would be calculated
from the slope of the fflacis : —

20 (a? — 3) » tiie distance from the crest of the glacis to the

crest of the parapet.
- 33' -f 5(y -f- 3',-f 6' -f (20 -f a? - 4) -f 24,
or « - 10*1 feet.

In other cases the profile of the rampart and ditch may be
given, and it may be necessary, as in Fig. 3, so t6 construct the
counterscarp and covered way, that the escarp may be screened
without giving a greater height than 1 2 ft. to the crest of the glacis.
The slope of the glacis must then be determined by the artillery
fire from the rampart.

The Trace.

234. Whether the obstacle in the ditch be water or a wall, it is Flank defence,
necessary that it should be actively defended. If the besieger is
unmolested it will not take him long to bridge the water, or blow
down the wall. Flank fire is at once the most effective mode of
defence, and the most economical of men and guns. Hence in
permanent fortification fiank defence is always provided for the *
ditches, and the works are traced with a view to this.

The line of the escarp is therefore taken as the magistral or Magistral,
guiding line of the trace ; or rather, as the face of the escarp may
be sloping, the line of the top of the escarp. This is often termed
the cordon^ from the rounded coping-stone which is sometimes
placed at the top of revetment walls. (Fig. 2, PI. III.)

Flank fire may be furnished either from the parapet of the Parapet flanks
rampart, or from casemates nearly on a level with the bottom of wid casemate
file ditch. The grazing fire of the latter sweeps the ditch more ^ ''

148

TERMANENT FOBTIFIOATION.

The three
traces.

thorongbly than <he i)lunginfl: fire of the former. Also the men
nnd guns in casemates are sheltered from enfilade or high-angle
fire, and can be kept in constant readiness to meet an assault;
Avhile parapet fianks can be seen from a distance, and can
usually be enfiladed. On the other hand, however much parapet
flanks may have suflfered from the besieger's fire, it will almost
always be possible to occupy them with infantry or field guns at
the moment of assault ; but if the front walls of casemates are
breached, whether by direct or indirect fire, they will seldom be
tenable. The inconvenience ^caused by the smoke in casemates
was for a long time held to be a serious objection to them,
especially for artillery ; but experiments have shown that this may
be got rid oF by proper construction.

235. There are three varieties of trace suitable for flank
defence : —

(1.) The tenaille, or star, trace, in which the salients and

re-entering angles are alternate.
(2.) The bastion trace, in which they are not alternate.
(3.) The polygonal trace, in which there are no re-entering

angles, or only very obtuse ones.

Tenaille trace. 236. In the tenaille trace (Fig. 1 , PL V.) the re-entering angles

should be between 90*^ and 12(r for effective flanking, and con-
sequently for an enclosed enceinte the salients must necessarily be
acute, and ill-defended as regards frontal fire. This trace has
nevertheless been adopted in several systems of fortification
{e.g. Montalembert), because of the powerful flank fire afiTorded not
only upon the ditch but upon the glacis. Its chief disadvantages
are that from%he acuteness of the salients the faces can be easily
enfiladed and taken in reserve, and the interior space between
them is confined ; that the flank defence of the ditch from the
ramparts is imperfect on account of the dead re-entering angle ;
and that if casemates are placed behind the escarp to defend this
dead angle they can be destroyed by distant batteries placed on
the prolongation of the ditch. It is more suitable, therefore,
for wet than for dry ditches, as with wet ditches the dead angle
is smaller, since the surface of the water is usually not much
below the plane of site ; and casemates, for the same reason, can be
less well hidden, whatever the trace, so that their advantages over
parapet flanks are much less marked.

237. In the bastion trace (Fig. 2, PI. V.), the two re-entering
angles opposite to each other afford the means, if they are far
enough apart, of seeing into the dead ground of the ditch from
the parapet. Each flank defends the half curtain (D/ or/ E),
the lace (AC or FB), and flank of the bastion opposite to it.

To assign the best dimensions to the bastions and to place
them at the requisite intervals, it is usual to consider separately
each portion of the rampart included between the most prominent
salient angles of two bastions — that is, two half bastions and the
rampart joining them. For it is evident that the completeness of
the defence of the escarps will depend on the mutual arrangement

Bastion trace.

II BB 1 1 II ( [_]^j^_r]°5_L

(^ : to jxtgs M9,

DAageriield.Lith 23. Bedford. St Covent Gtirden

ELEMENTS OP PEKMAKENT FORTIFICATIOX. 149

and proportions of those parts ; besides which, in adapting forti-
fications to irregular sites, it is generallj found more convenient
to fix the salients first. Each of the above-mentioned portions
(as A D E F B, Fig. 2) is called 9, front of fortification.

That the whole curtain may be defended, tbe flanks of the
bastions, if not casemated, must be so far apart that the lines of
their musketry fire, when depressed as much as is admissible, may
intersect within 3 or 4 feet of the foot of its escarp. Every part
of the bottom of the ditch will be thus sufficiently defended. The
length of the curtain should therefore, in such a case, depend Leugtb of
upon the relief of the flanks and the greatest admissible depression «"''**>"•
of musketry fii-e. We will suppose these to be fixed, and that
it is required to find the length of the curtain. Let a by Fig. 3,
be the profile of the flank CD. From the crest a draw a line
inclining downwards at the greatest admissible depression of
musketry fire, which may be taken at ^, and produce it till it
meets the line b y, drawn 4 feet above the bottom of the ditch,
at 6?; b d will be the distance beyond which the musketry fire of
that flank will defend the ditch. Draw ef on the plan parallel
to CD, at a distance from it equal to b d^ and it will mark the
intersection of the plane of musketry fire with a plane of 4 feet
above the bottom of the ditch. The whole of the curtain to the
right of the line ef will be defended from the flank CD, and if
both flanks have the same relief, and the bottom of the ditch is
horizontal, D/ will be half the curtain. If not, the distance /E
may be found in the same manner as D /, by constructing the
section y z of the flank EF. From this it is evident that if the
curtain is so short that the lines of fire from the flanks intersect
at a point more than 4 feet above the bottom of its escarp, there
will be in front of it a space undefended from the parapet, the
extent of which is shown by drawing lines, as above, parallel to
each flank. Casemates, however, may be constructed in tlie flanks,
as shown in Fig. 8, PI. III., having embrasures and loopholes,
by means of which the whole of the ditch may be flanked, how-
ever short the curtain may be.

In order that the faces of the bastions may also be completely Length of
defended, their length must be limited by that oF the lines of ^^'
defence ; that is, the flanked or salient angle of each bastion must
not be too far from the flanks which defend it. Until of late
the maximum length of the lines of defence of fortresses has been
considered to be 300 yards, in order to keep the salients flanked
within effective range oT case and musketry from the flanks.
This limit, owing to the improvements in artillery and musketry,
may now be extended to 500 yards, although at that range there
will be some loss of effect.

On the other hand, owing to the relief which it is necessaiy
to give to the ramparts, and the consequent length of the curtain
when defended from the parapet of the flanks, if the line of
defence were made less than about 280 yards long, the face of the
bastion would be too short, and the bastion itself too small for
effective defence. In a bastion such as E F ^ A ?, Fig. 2, PI. II.,

150

PBBMANENT J^ORTIFICATIOK

Length of
flanks.

Construction
of fronts.

pi. II.

the besieger's shells would be extremely destmctiye, owing to
the small interior space, and the consequent crowding of liie
defenders. A breach in the face F g would throw open its whole
interior, and the defenders would hardly have room to show a
larger front than a storming party at the summit of the breach.
It is necessary, therefore, to lay down a minimum, as well as a
iinaigiTmiTn, length for the lines of defence, and they are generally
made not less than about 280 yards long.

The length of the front should thus be determined by the
lengths of the curtain and of the lines of defence. It is evident
that by merely altering the angles which these lines form with
each other, without materially altering their dimensions, the
length of the flanks may be increased or diminished. It is of
the utmost importance to expose the faces of the bastions as little
as possible to an enemy's enfilade fire, to keep the bastions from
being cramped, to have frontal fire on the capitals, and to
preserve the interior space ; they are inclined inwards, therefore,
only just enough to afford room in each flank for as many guns as
the besieger can mount on the crest of the glacis opposite to it,
for the purpose of silencing its fire.

238. The usual mode of tracing the bastioned fronts of a fortress
is to surround the space to be defended by a polygon. The length
of its sides are suited to the features of the groimd and to the
jequired extent of each front, which, with the ordinary relief
would be not less than about 380 yards. The required con-
ditions are then fulfilled by the following construction. Bisect
the side of the polygon AB (Fig. 2), and draw GH perpendicular
to it If the polygon has more sides than five, make GH equal
to one sixth of AB. If the polygon be a pentagon or square the
perpendicular will be equal to one seventh or one eighth respec-
tively, so as not to reduce the salient angle of the bastion more
thaii can be helped. Through the point H draw the lines of
defence. Make the faces of the bastions AC, BF, equal to one
third of AB. From the points C and F draw the flanks at
right angles to the lines of defence BD and AE. Draw the
curtain joining the inner ends of the flanks. By drawing lines
in prolongation of the curtains an interior polygon is formed, the
sides of which, as YZ, are termed interior sides. The outer
polygon is, in contradistinction, called the exterior polygon, and
its sides exterior sides. The line GH is called the perpendicular.
The angles ABF, BAG,* are termGdi diminished angles; ACD,
BFE, angles of the shoulder ; ODE, DEF, angles of the flank;
AHB, angle of the tenaille. If the position of the interior side
only is fixed, draw tlie curtain first, proportionate in length to
the distances bd^ (Fig. 2), determined as above from the
profiles of the flanks, so that it may be duly defended. Draw
/ H from the centre of the curtain perpendicular to it, its length

* In old fortresses flanks are often found provided with orUlona — ^rounded or
angular projections at the shoulder (N, Fig.' 2), to shelter the guns, especially at the
outer end of the flanks.

ELEMBNtB OF P^RMAKfiKl' PORTtFlCATION 151

being in the same proportion to that of the curtain as GH is to
AB. Draw the lines DB and EA through H^ and the flanks
perpendicular to them at the extremities oF the cui*tain. The
lines DB and EA are made of a length that is suitable to the
form of the ground, and that will give good proportions to the
bastion^, but not less than about 280 yards.

If the flanks are casemated (Fig. 8^ PI. III.) and the curtain is
consequently shortened^ at the sacrifice of complete defence from
the parapet, the lines of defence may be reduced in length.
On the other hand, if the site permit the use of very long lines of
defence, and there is therefore no danger of the faces of the bastions
being too short, the diminished angle may be 1 ^sened, and the
curtain lengthened sufficiently to afford room for a flank of the
usual length.

Although in the foregoing construction thie flanks are drawn Direction of
perpendicular to the lines of defence, this need not always be the ^*^^«-
case. Vauban preferred making their extremities C and D, F and E,
(Fig. 2) equidistant respectively from the opposite shoulders F
and C ; and modem French engineers both in theory and practice
have adopted a similar construction. By doing so, a flank fire U
more easily directed along the escarp of the curtain, which has to
be defended as well as the line of defence, and both curtain and
flanks are increased in length — advantages which more than
counterbalance the reduction in width of the gorge of the bastion.
It should be remarked, however, that the interior crest line of a
permanent work is not necessarily parallel to its escarp. There
would, therefore, be no difficulty in so arranging the crest of the
flank, that while part is perpendicular to the curtain, the remainder
.may be thrown back so as to be perpendicular to the line of
defence.

289. It is evident that any breach formed in the escarps of the Tenalile.
flanks and curtains would render useless all retrenchments in the
bastion, and that the great width of the ditch in front of them
exposes them to breaching, even by distant fire. A small work,
therefore, called the TenaiUe (a 6, Fig. 1, PL IX.) is often placed
in the ditch in front of the curtain and between the flanks, to
cover their escarps. Its magistral line coincides as far as may
be with the lines of defence, and its width is from 15 to 17 yards.
It is completely detached from the body of the place, its ends and
gorge being usually kept at a distance of about 1 1 yards from
the escarps of the flanks and curtain. As to profile, the crest
of the tenaille must not be so high as to prevent the flank
from defending a breach in the face of the opposite bastion, or to
create a dead angle in its own front.

It was formerly revetted on all sides, anl provided with a
parapet and banquette, so that it might be occupied by infantry ;
but more recently it has been treated as a mere screen or mask,
and left unrevetted except at the ends.

Besides covering the walls of the flanks and curtain, the tenaille
protects the communication through the curtain ; and by providing

152

PERMANENT FORTIFICATION.

Polygonal
trace.

Broken out-
wards.

Broken in-
wards.

Short fronts.

Caponiers.

a secure place of assembly between itself and the curtain, it greatly
facilitates sorties in the ditch.

On the other hand, the tenaille shields the space between its
ends and the flanks of the bastion from the fire of the opposite
flank, and renders it diflicult to flank the main ditch by meaas
of casemates.

240. In the polygousd trace the flank defence is necessarily from
casemates, and the conditions imposed by it are consequently
much less rigid. The length of fronts may vary up to 1,000 yards,
or twice the extreme limit of the line oi defence. The flanking
works are either caponiers or counterscarp galleries ; but the latter,
on account of their exposure to attack by mining, are seldom
relied upon for the main ditches of works that are likely to be
regularly besieged. With long fronts the caponier is commonly
])laced in the middle. The half fronts on either side of it may be
in one straight line (Fig. 3, PI. V.), or they may be broken out-
wards or inwards, so as to form an obtuse salient or an obtuse
re-entering angle (Fig.-*. 4 and 5).

By breaking them outwards it will usually be made more
diflicult for the enemy to place batteries on the prolongations of
the ditch, and so to breach the caponier from a distance; and as
the angles of the polygon thus become larger, it will also be more
diflicult for him to construct breaching batteries on the counter-
scarp at these angles.

By breaking them inward?, the caponier is better protected
against the enemy's direct advance upon it, as the half-fronts
give a convergent fire upon the ground in front of it, making
the progress of the approaches slower, while the distance to
be traversed is increased. This advantage, however, would not
be worth securing at the cost of greater exposure of the caponier
to distant artillery fire along the ditch.

With short fronts, as in the case of detached forts, the caponier
will usually be hest sheltered by placing it at the junction of two
fronts, whether it is required to flank both of them or only one
(PI. XV.). This portion may sometimes be adopted even with
long fronts, the fronts being broken inwards, where it would .
otherwise be impossible to prevent the enemy from taking up the
prolongation of the ditch (Fig. 6, PI. V.).

241. Caponiers have been made with two or even three tiers of
casemates, and sometimes with a large number of guns in each
tier, and with barrack accommodation for a battalion. In sucii
cases they have had an open terreplein on the top for musketry
or artillery, with an earthen parapet, and an interior courtyard
separating the two flanks, but since the introduction of curved
fire their size has been reduced for all works with dry ditches.
The width of th.e ditch will now seldon) allow it to be swept by
more than four guns in one tier, and upper tiers have been for the
most part abandoned, as they cannot be properly screened. Instead
of being organised with a view to overpowering the besiegers

♦ An example of the application of poweif ul caponiers to wet ditches w given m
the Antwerp front, page 176.

Inngsrfield' Uih 22 Bf dford 3'

ELEMENTS OF FEBMAKENT FORTIFICATION, 163

batteries on the counterscarp by the number of their guns^ they
:are now more strictly reserved for sweeping the bottom of the
<ditcb^ and carefully hidden^ by profile as well as by position^ so
that they may remain uninjured up to the last stage of the
tiefence.

PL XVL, and Fig. 5, PI. XV., show a central caponier and a Small ct^
-shoulder caponier for a small detached '/ort, with a ditch only P®°*«"'
10 yards wide. If they are to be armed with artillery, the gun-
rooms cannot conveniently be less than 12 ft wide and 16 ft.
long ; for mitrailleurs or musketry much less space is necessary.
Allowing 9 ft. to the crown of the arch, and 6 ft. for the brick-
work and concrete of the arch, the necessary height of the outer
ivall is 15 feet above the bottom of the ditch, and above this there
must be at least 6 ft. of earth. If this height would involve
exposure to curved ^re, or if it is thought desirable to raise the
floor level above the bottom of the ditch, about 3 ft. may be saved
by having a flat roof of concrete on iron girders, instead of the
.arch. ^

242« Gunports for guns on casemate platforms or common GnnportB.
garrison carriages should have their sills 2 ft. 6 ins. above the
^oor, and should have a width of 2 ft. at the neck, and a height of
2 ft. 6 in?. The neck is usually placed about 2 ft. from the back
of the wall^ and the cheeks in front and behind this are splayed
according to the lateral range required (Fig. 3, PI. VI.).

In musketry loopholes the neck is a narrow slit, seldom less Musketry
than 12 in. X 2. in., and sometimes longer. Loopholes are distin- loopholes,
^uished as vertical or horizontal^ according to the direction of this
elit (Figs. 1 and 2). Horizontal loopholes are used chiefly for
frontal fire across the ditch, where lateral range is desirable ;
vertical loopholes chiefly for flanking fire, where the lateral range
is limited, and great depression may be needed. Occupying little
width of wal^, they can be placed on either side of gunports in
casemates. Where both lateral and vertical range are needed,
horizontal loopholes may be combined with machicolations (Fig. 4).
In thin walls the neck may be on the outer face, but in walls
more than 3 ft. thick it is best to place it about 2 ft. from the
back of the wall, and at such a level that the line of fire with the
utmost required depression shall correspond to the height of a
man's shoulder. To avoid splinters at the neck it is well to form
it with bullet-proof iron, and to build the cheeks on the outside
in offsets, so that bullets may not glance in.

243. The widening of the ditch opposite the caponier necessarily Escarp gal-
ieaves the escarp alongside of it less well screened than elsewhere. the^aponier5
As the caponier is itself flanked by galleries behind this escarp, it
is very important that it should be protected ; the increased width
should therefore be no more than is absolutely necessary, and the
glacis should, if possible, be raised correspondingly (see Fig. 1,
PI. XV.). Care should also be taken that if the top of the escarp
is destroyed it shall not bring down the parapet^ or mask the
flanking loopholes^ or give the enemy facilities for escalade.
Partly on this account, and on account of the lowness of the

42642. • I.

154 PEBMANENT FOBTIFIGATIOK.

caponier, a drop ditch, 6 ft. or more in depth, is often carried round
the caponier and along its flanking galleries (Fl. XYI.)> adding
to the height to be climbed here, and serving as a receptacle for
the debris from the upper part of the wall. This ditch also pre-
vents the enemj'from closing upon the gunports and loopholes
when thej are not much above the level of the main ditch. The
drop ditch, however, must not offer dead angles in which the
enemy could remain unharmed. Where such angles cannot be
seen into from loopholes, either escarp or counterscarp, inclined
flues may be made in the wall above them, down which shells or
grenades can be rolled ; or direct view of the base of a wall may
be obtained by means of machicolations, an arch being turned in
the wall at the level of the floor of the gallery behind it, and the
brickwork imder the arch being set back at a slope (Fig. 4, PJ. VI.,
and Figs, 2 and 3, PL XVI.).

Detached 244. It is sometimes better to disconnect a caponier from the

caponiers. niain escarp, so that if it is breached or escaladed it may not give

the enemy admittance to the body of the place. This is the case
especially on important fronts, where the caponier is likely to be
attacked by mining, and the progress of the besiegers is to be
obstinately disputed to the very last. The escarp behind the
caponier should be retired, leaving a space 8 yards or more in width.
To separate this from the main ditch and prevent an assault on the
caponier from the rear, ridged walls may be carried across from
the caponier to the escarp (PL VII., ana Fig. 2, PL IX.).-.
Masks. 245. Even where fronts have been so traced that, owing to the

obtuseness of their salients, or to particular accidents of ground^
the enemy cannot establish batteries on the prolongations of the
ditch, to breach the caponier, he may still be able to eflect this by
means of oblique fire grazing the crest of the glacis, and striking
at an angle of not less than 54° (horizontally) to the line of the
caponier flank. The glacis is evidently a very imperfect screen
for the caponier against fire of this kind, especially for the end of
the flank that is furthest from it. Here, as in so many other cases^
iron plating is desirable, but^ owing to the cost, ean seldom be
provided. In default of it tunnelled masks may be adopted to
protect the gun casemates, while avowing the necessary angular
range for the guns. These masks may be either attached to the
front wall of the casemates, or they may be detached^ and separated
from it by an interval of several yards. Attached masks (PL VII,)
are more easily applied and obstruct the fire of the guns less ; but
they are more likely to cause inconvenience from smoke, they give
less protection against shots at slight angles of descent, and when
they have been partially cut down by continued firing, there is no
wail behind them, as in the case of detached masks^ to secure the
caponier against assault. In both cases the piers of the tunnel
arches are in prolongation of the piers of the casemates, though
they may be more solidly constructed ; the height of the arches
should not be less than about 8 feet ; the length and thickness
of the arches and their covering should be enough to demand a
very heavy expenditure of ammunition for their destruction, and

CAPONIER
WITH ATTACHED MASKS.

S/rfwri- fii A B

ELEMENTS OF FEBMANENT EOBTIKOATIOnJ 166

drop ditches should be provided to receive their d^bri8,"80 that
there may be no obstruction to the fire of the casemates in rear.

246* Ordinarily the earth cover on the top of a caponier is merely Open terre-
formed as a roof, but where the width of the caponier and the P^®™-
reliefs alike admit of it, parapets may be formed for musketry
(PI. VII.), which will be useful either against an assault or
against the besieger's counter batteries at the salients.

247. The head of the caponier can usually be defended by conn- Flank defence
tergcarp galleries, which will at the same time serve as a base for a of the head of
system of counter-mines to secure it against mine attacks (Fig, 2, *^® <»POM«r.
PL IX.). These galleries may be entered direct from the ditch,

or sometimes a special passage to them may be carried under the
ditch, so that the men placed in them may not have reason to fear
that their retreat will be cut off. But as, in a regular attack, the
counterscarp galleries are likely to fall before the caponier, some
supplementary defence is desirable, either from loopholes in the
head of the caponier itself, or irom loopholes in the escarp wall.

27ie Communications.

248. The importance of good means of issue for the garrison, Commnnica-
and the need that these should be well guarded and secured, tions.
have been already referred to. The communications with the
ground outside for ordinary purposes of defence consist of (1) the
postern under the ramparts ; (2) the passage across the ditch ;

(3) the ramps or stairs for mounting the counterscarp; and

(4) the sallyportSy leading out from the covered way on to the glacis.

(1) The postern is a tunnel, from 8 to 12 ft. wide, leading from Postem.
the interior of the place into the ditch. Its inclination should
not be steeper than ^, in order that it may be couvenient for guns.
Both ends are closed with gates. With a dry ditch its outer end
is usually about 6 ft. above the bottom of the ditch. It is some-
times provided with a drawbridge or rolling bridge, 10 or 12 ft.
long, counecting it with a causeway or a wooden staging on its
own level, or moveable steps may be used to descend into the
ditch. For better cover the postern itself may be brought to
the level of the bottom of the ditch, and in that case a drop ditch
is made in front of it. Where the ditch is wet it should be at
least 1 ft. above the highest level of the water.

In a bastioned front a postem is generally carried under the
middle of the curtain, so that its outer end is under the fire of
both flanks, and is hidden from the enemy by the tenaille.

Fig. 1, PI. VIII., shows the outer end of a postem provided with
a drawbridge. Such drawbridpres are of various design, but the
most important point is that they should be readily raised or
lowered by two or three men, and that the counterweights pro-
vided with a view to this should vary as the leverage of the bridge
varies, so that the balance between them may remain constant. In
the example given this is approximately the case. Chains of
heavy cast-iron links form the counterweight, and as the bridge
rises the weight of these links is successively taken ofiP. The
motion is given by means of an endless chain.

L 2

156

PEHHANENT FORTIFICATION.

Caponiers.

Vaulted pas-
sages.

Ramps.

Stairs.

Ditch traverses. (2) It is often unnecessary to provide any coyer for the passage

across the ditch^ but where the ditch is likely to be enfiladed some
protection is needed. In such a case a traverse is usually formed,
on one or both sides as may be necessary* high enough to defilade
the communication, and with a gentle glacis for its exterior slope
so that it can be swept by the defenders' fire from the rampart.
Such traverses are sometimes provided with banquettes, and
called caponiers, although they are now of little value for flank
defence.*

A double caponier is made to protect the passage from the
tenaille across the main ditch in a bastioned front' {c e, Fig. I,
PL IX., also Fig. 2, PI. VIII.), an interval, from 8 ft to 12 ft. wide,
being left for the roadway between the two parapets.

In special cases it may be worth while to have a vaulted pass-
age of masonry well covered with earth, or to tunnel under the
ditch, but all unnecessary descents and ascents in the communica-
tions should be avoided. With wet ditches, bridges and dykes,
or, in their absence, boats, must be used.

(3) Easy ramps should be provided for mounting the counter-
scarp. Their width should be from 8 to 12 ft; meir slope not
steeper than -J-, and less, if possible, wherever the height to be
ascended exceeds 10 ft.

Stairs are often useful in addition to ramps, and sometimes
necessary as their substitutes, where ramps would be too long.
But they are practicable for infantry only, and are liable to be
destroyed by high-aDgle fire. They are usually made 6 ft. wide,
with a rise of 8 ft., and a tread of 12 ft. to each step ; but the;^
may be narrower and steeper if need be.

In long ramps or stairs it is advisable, in order to prevent the
enemy from making use of them, to have gaps, about 12 ft. long,
which are temporarily bridged over with planks (Fig. 3, PI. VIII.),
or the base of the ramps or stairs maybe enclosed with a palisade,
provided with barrier gates.

(4) To pass from the covered way out on to the glacis, ramps
are cut through the interior slope. These are also closed by barrier
gates, and are called sallyports (Fig. 4). They are especially
placed in parts of the covered way that have been widened out to
form places of arms, in which troops can be massed. Sometimes
the interior slope of the glacis is itself made gentle enough
(scil. J) for 30 or 40 yards, to allow infantry to advance up it.

Main entrances. 249. Besides the communications required for defence, there are

always some main entrances by which the great roads of the
country pass into the fortress. These should as far as possible
be placed upon the most secure fronts. They consist of an arched
gateway, not less than 15 feet wide, provided with a guard room
and barrier gates, and connected by a moveable bay about 12 fl, long

Sallyports.

* It was formerly usual to blind the passage, so that it formed a loopholed
musketry gallery, much like a field caponier. Caponier is from caponera (Spamah),
a hen coop. It was applied to wooden, earlier than to masonry, galleries.

^U 1 P>^t>-in

(■Snii,- ^, fl„-FUj.t. :.'/},-!

nuigtrliaia liih JJ.BMford El

ELEMENTS OF PERMANENT FOBTIFIGATION. 157

^th a fixed bridge which carries the road. The moveable bay may
be either a drawbridge, which is drawn up and closes the gate-
way, a rolling bridge, which is drawn inward behind the barrier
gates, or a drop bridge^ of which all or part falls below the level
of the roadway.

The road after reaching the outer side of the main ditch is often
led through various outworks, each with its own barriers, for
greater security. (See Porte des Pierres, PI, XIII.)

Ouitoorhs.

250. Besides the covered way, and the tenaille (which is pecu- Outworks,
liar to the bastioned trace), other outworks are sometimes added
to strengthen a front, either by interposing directly on the line of
the besieger's advance, or by bringing a fiank fire to bear upon
him as he advances on some other line. Of these the most im-
portant are ravelins and counterguards,

A ravelin is a redan, or occasionally a lunette,* placed opposite Ravelin,
the middle of a front (rf, e^f, Fig. 1). It is intended to serve the
following objects : — -

(1.) As a bridgehead to cover a road leading out of the
fortress.

This was one of its earliest purposes, and as when so used it was
often made semicircular, it was also termed a demi-lune, a name
which it still bears in France. . ^ i i .

(2 ) To protect the central part of a front, and make it more
difficult to breach this part, since a breach, if made here,
can be less easily retrenched-
(3.) To shelter the central caponier in a polygonal front, and the
flanks in a bastioned front. It should, therefore, in the
latter case, be wide enough at the gorge to overlap the
shoulders of the bastions, so that they may not be breached,
and the flanks consequently be laid bare.
(4.) To bring a flank and reverse fire upon the besieger as he
advances upon the salients of the body of the place, and so
to delay this advance, and oblige him to attack the ravelin

first. • J- 1

(5.) To intercept if possible the prolongations of the mam ditch

and rampart of the neighbouring fronts, and so make it

more difficult for the besieger to enfilade them.
For the two last objects it is desirable to give it as much
saliency as the width of its gorge will allow, without reducing its

salient angle to less than 60**. , . ^ . r

A large ravelin has the further advantage that it admits ot a

better retrenchment and a more vigorous defence ; but it naust

not so completely cover the front that its glacis is ill-flanked

from the body of the place.

It will be seen that a ravelin gives to a bastioned or polygonal Defecte of

front something of the advantages of a tenaille trace. But with traee.

these go the corresponding defecte.

* In this case it is sometimes called a detached bastion.

158

PJBBHANENT FOBTIPIOATIOK.

Flank defence
of the ditch.

By casemates.

Profile.

Keep.

Counter-
guards.

The faces are almost always exposed to enfilade5 and must be
provided with numerous traverses. To lessen their exposure and
bring their fire to bear in the directions where it is most needed,
it is best, where space allows, to break them back from the escarp
line, forming a casemated battery at the salient (Fig. 2).

The ditch offers gaps through which the besieger may breach
the escarp of the body of the place, and its flanking works are not
easily secured from (fistant fire. On bastioned fronts it is usually
flanked from the rampart of the bastion faces, but those faces can
often be enfiladed, or at all events can be silenced by frontal fire.
Glacis traverses (or caponiers) are usually placed at the ends of
the ditch (I I, Fig. 1) ; they do away with the dead ground that
there would otherwise be here, owing to the height of the parapet
of the bastion ; but they cannot be made high enough to screen
the escarp of the bastion effectually, and they cannot be brought
close up to the escarp of the ravelin as they would assist escalade.

Where casemate flank defence is employed, as in polygonal
fronts, the* casemates must either be placed at the salient, where
they are exposed to mining, or they must be well protected by
masks or iron against curved fire. They may be attached as wings
to the ravelin, or (as shown in Fig. 2) they may be placed behind
the escarp of the body of the place, firing through tunnels in a
traverse overlapping the ravelin. If this traverse is made high
enough to screen the escarp thoroughly, the fire from the main
rampart will be able to defend very little of the ditch of the
ravelin, but it will nevertheless be able to oppose the counter-
batteries which the besieger may make opposite the salient of the
ravelin with the view of destroying the flanking casemates.

As regards profile the crest of the ravelin must be at least 6 feet
above that of its glacis, and at leagt 3 feet below the crest of the
body of the place. In order that it may not interfere with the
fire from the latter upon the ground in its front, the difference of
relief should if possible be much greater. An escarp wall, though
usual, is much less essential for this and other outworks than for
the body of the place, as the besieger, if he carries them by assault,
has little chance of being able to maintain himself in them, unless
he has already brought his trenches of approach close up to them.

A keep or r4duit is often provided for the ravelin ; on bastioned
fronts this is usually a large open lunette {ghi, Fig. 1), pn poly-
gonal fronts usually a casemated work covering the caponier, or it
may be the head of the caponier itse^. But casemates that are
able to see the whole interior of the ravelin, are exposed to
destruction by curved fire. It is probably better, therefore, to
form a glacis at the gorge which will screen the caponier, and
which can be swept by the fire of the body of the place.

251. Counterguards are works intended to protect the faces of
bastions in the same way that the tenaille protects the curtain
{see^ Why PI. XIII.). They may be applied also to polygonal fronts,
or, if necessary, to ravelins, or to caponiers. Besides covering the
escarp of the work behind them, they also furnish a lower tier of
fire. When they are so narrow as to be suitable only for musketry

ELEMENTS OF PEBMANENT FORTIFICATION. 159

they are termed couvrefcLces ; such narrowness has the advantage
that the besieger has no room to establish breaching batteries
upon them.

Counterguards are chiefly useful —

(1.) Where the ground falls steeply to the front, so that it would When osefnl.
be diMcuh to screen the escarp of the work in rear by means of
the glacis. In such a case aleo th^ site makes it easy to give the
difference of command necessary for the simultaneous fire of the
two works.

(2.) With a wet ditch, when that is not in itself a sufficient
obstacle, and an escarp wall is provided. On account of the width
of a wet ditch the escarp wall cannot be properly covered by the
glacis, and therefore a counterguard behind the main ditch,
separated by a narrower ditch from the escarp, is of great
advantage.

Under ordinary circumstances counterguards are not worth Their ordinary
providing, because of their cost, and because, by considerably disadvantages,
increasing the distance between the main work and the glacis,
they lessen the effectiveness of the fire from the former, and
heighten the command required for it.

When several counterffuards are connected together they con- Flank defence
stitute an envelope ; but if this envelope is strictly continuous and oi their oitcnes.
self-flanking, its ditch, when the besieger has captured it, gives
him useful cover for troops in his further operations, as it cannot
be seen into from the place. On the other hand, if gaps are left
at the re-entering angles to allow the ditch to be flanked by the
works in rear, the escarps of these works may be breached
through these gaps. It is in any case seldom worth while to
build an escarp wall for a counter-guard, and, therefore, on
account of the difficulty attending the flank defence of its diich,
it may be better, instead of a steep exterior slope, to form a gentle
glacis which can be swept by the frontal fire of the work behind
it, and upon which field obstacles can be disposed if necessary. In
fact, the inner glacis^ which has been already mentioned in
speaking of the covered way (paragraph 231), will usually be
cheaper and better than a counterguard,

252. The re-entering angles of a front are the best points for Places of arms,
the issue and retirement of sorties. Accordingly, in these parts
the crest of the glacis is thrown forward so as to form re-entering
places of arms in which troops can fee assembled. In a bastioned
front without a ravelin the re-entering place of arms is opposite
the curtain; in fronts with ravelins there are two, one on each
side of the ravelin {p /?, Figs. 1 and 2), provided with sallyports {q q ),
At the salients also, owing to the rounding of the counterscarp,
there is some enlargement of the covered way, and the spaces
so formed are called salient places of arms (s 5, Fig. 1). The
intervening portions are called the branches of the covered wag.
Traverses (t t) are carried across the covered way to enclose the Traverses of
re-entering places of arms, and sometimes also at intervals along *^® covered
the branches. They are made of the same height as the crest of ^*^

160

FEBHANENT FORTIFICATION.

Keep of the
re-entering
place of arms.

Plantations.

the glacis^ and are provided with banquettes for musketry, and
usually palisaded. Passages 7 feet wide, provided with barrier
gates, are carried round the outer ends of these traverses, tho
crest of the glacis being indented to allow of this. The traverses
are intended to give protection against fire enfilading the covered
way, and to allow a stand to be made at each, successively, aftei
the defenders have been driven out of the salient places of arms.
They give less protection, however, against the fire of rifled
guns than they did against the ricochet fire of smooth-bore guns,
and they obstruct the movement of troops along the covered
way, and the flanking fire along it from the ramparts. In the
branches of the covered way, therefore, traverses are now usually
suppressed. To hinder enfilade the crest of the glacis may be
traced with crotchets (or indented, v. PI. X.), unless the jirotection
of the escarp should make it necessary to keep it as close as
possible to the counterscarp.

To assist the defence of the covered way, or to cover the with-
drawal of the defenders, a keep is usually provided for. the
re-entering place of arms, and sometimes also in the salient place
of arms. The keep, or r^duit, of the re-entering place of arms is
sometimes an open work (r. Fig. 1), and sometimes casemated.
If an open work, its parapet must have a comnoand of about
3 feet over the crest of the glacis. If casemated, it should be
entirely hidden fi'om the besieger's view, and the masonry
screened as far as possible from curved fire. A simple masonry
blockhouse loopholed for musketry, defending the interior of the
place of arms and the head of the ramp leading into the main
ditch (r. Fig. 2), is perhaps now the best form of keep. It may
be applied also to the salient places of arms. There should be an
underground passage for communication with it, which' may be
in connexion with the countermine system.

253. Trees are often planted on the glacis of fortresses, and
when judiciously placed will prove a valuable aid to the defencCr
Being cut down when the place is about to be attacked, they
will afford a supply of timber just when it is much needed, and
the roots running under the surface of the glacis in all directions;
will much impede the construction of the besieger's saps. Care
should be taken to leave a space of about 20 feet clear in front of
the crest. This part will be of no use to the besieger, as the sap
of his lodgment will probably be excavated outside of it. The
defenders may have occasion during the siege to cut ramps in
it ascending from the covered way to facilitate sorties, or to
construct lodgments thereon for riflemen. For the same reason
it would be advisable to avoid planting any parts of the glacis
where it is likely the defenders vnll have to excavate counter
approaches.

Interior de-
fenees.

Retrenchments.

254. When a breach has been made in the body of the place,
a retrenchment is, if possible, prepared behind it, so that the

ELEMEXTS OF PEBMANENT FORTIFICATION. 161

besiegers^ after mounting the breach, may neither be able to
penetrate further iivvrards, nor to extend hiterally along the
ramparts. Even though unable to offer any prolonged resistance,
the support afforded by a work of this kind will allow the breach
to be more vigorously defended. But as it is difficult to im-
provise such a work satisfactorily during the course of a siege,
and under exposure to the enemy's fire, it is sometimes provided
beforehand, either in whole or in part, for those parts of the
enceinte which are especially likely to be breached.

Bastions, for instance, often have permanent retrenchment s, Bastion re-
the extremities of which may rest either upon the faces, the trenchments
flanks, or the curtain. Those resting on the faces reduce the
space surrendered to the besieger, and preserve the flanks, but
they may be turned by breaches at the shoulders. Those resting
on the curtains cannot easily be turned, but they leave the
adjacent bastions without flank defence. Those resting on the
flanks retain some portion of these for the garrison, but it is
possible that tliey may be turned by breaches in the curtain at
the ends of the tenaille. Where the length is sufficient a bas-
tioned trace may be given to the retrenchment (v. Fig. 1, PI. 9),
or it may be flanked by casemates, and traced so as to give a
convergent fire upon the breach.

The character and position of a retrenchment will to some Full and
extent depend upon whether the bastion is full or hollow, that is, ^p^^^ ^»8-
whether the whole of the interior has been brought up to the ^^'
level of the terreplein of the rampart, or whether (as in the left
bastion of Fig. 1) it is considerably below it. Full bastions are
more easily retrenched during the siege, and are more favourable
for a step-by-step defence. With hollow bastions it is of more
importance that the retrenchment should be placed where it
cannot be turned, and therefore at the gorge.

Full bastions often contain cavaliers (v. the right-hand bastion Cayaliers.
of Fig. 1), with faces and flanks parallel to those of the bastion,
but several feet higher, so as to give a more plunging fire upon
the glacis, and perhaps to see ground that would otherwise be
hidden. In such cases the retrenchment is made by cuts or
coupvres across the faces of the bastion near the shoulders. The
inner ends of the ravelin are often retrenched by similar
coupures (Fig. 1).

Cavaliers protect the flanks and faces from reverse fire, but as Defects,
retrenchments they have two great disadvantages. They cramp
the interior space of the bastion, hindering freedom of move-
ment, and they suffer equally with the bastion from the fire of
the besieger's batteries, arresting and exploding shells that would
otherwise pass clear, and thus adding to the losses upon the terre-
plein below.* The same disadvantages apply in some degree to
bther permanent retrenchments. It is hardly possible to dispose

* The fausse braye, which consisted of a second terreplein and parapet, phiced
below and in advance of the main parapet, and which was at one time largely
adopted, has fallen into disuse chiefly owing to this inconyenience of successiye tiers
of earthen parapets.

162

PEBHAKENT FORTIFICATIOK*

Bomb-proof
coyer.

Main powder
magazines.

Essential
points in per-
manent works<

them so that they shall be unobstructive during the earlier stages
of the defence^ and undamaged when their own stage arrives.
Often, therefore^ instead of an extended retrenchment^ a nucleus
only is constructed beforehand, in the form of a defensible barrack,
or merely a blockhouse. Besides retrenchments on particular
fronts^ many fortresses are provided with citadels, serving as a
retrenchment for the whole place ; and in the same way important
detached forts are provided with keeps.

255. Recent experience shows that before undertaking the
labours of a regular siege, an enemy vrill now usually naake trial
of the efficacy of a heavy bombardment, and places ill-provided
to meet this have been brought to surrender in a very few days.
In any case^ the vigour and heartiness of the defence will depend
greatly on the secure and unbroken rest which the troops may
be able to get when they are off duty. Ample bomb-proof cover
is therefore of the first necessity, and in so far as the casemates
under the ramparts, or independent casemated barracks may be
insufficient to furnish this, they will have to be supplemented by
blindages hastily prepared when the place is attacked^ and when
there is much else to be done. The general requirements, not
only for the troops, but for the stores and provisions for a long
defence, should be carefully estimated, and met as far as possible
beforehand, and a margin left for casemates which may become
untenable, according to the particular direction of the attack.

The main powder magazines should be placed in the most con-
venient and sheltered situations that can be found for them, re-
moved from other buildings, and abundantly protected with
earth. To guard against damp their walls are built hollow, and
great care must be taken that the magazines are not left open
and the outside air admitted, except when its dryness and tem-
perature are such that it will absorb rather than deposit moisture
on the cold walls of the magazines.

Recapituldiion,

256. To recapitulate, the main points to be studied in the design
of permanent fortifications are briefly as follows : —

1. That the artillery on the rampart should be able to concen-

trate a heavy fire in any required direction.

2. That it should be difficult for the besieger to avail himself

of enfilade fire to silence this artillery.

3. That where the main obstacle to assault is an escarp wall,

this wall should be protected, not only against direct, but
against curved fire, up to an angle of descent of J.

4. That this obstacle should be well flanked, and that the

flanking works should not be capable of destruction, at
all events from a distance.

5. That the communications with the outworks and with the

country should be simple, easy, and safe.

6. That outworks and retrenchments should be applied to

give additional strength to the enceinte, wherever they
may be needed.

— *w

l^cS

SecbLorv orv a.b

Opp . bojxjuge /fi^-

Dangerfield. Lith.22. Bedlbrd S^ Caronl Garden.

ELEMENTS OF FEBMANENT FOBTIFIOATION. 163

7. That there should be ample bomb-proof cover as a security

against bombardment.

8. That mine attacks should be adequately guarded against, and

countermines used offensively against the besieger. This
subject will be treated of in a later chapter.

These points are far from depending wholly upon the general Comparuon
trace, some of them are mainly questions of detail organization. ^*![®*^^^®a
But the influence of trace is considerable, and it will be well to the polygonal
compare in relation to them the two chief traces, the bastioned trace,
and the polygonal.

It has been already pointed out that with equal lines of defence
the polygonal trace gives longer exterior sides, as the lines of defence
do not overlap. For instance, if these lines are limited to 280
yards, the exterior side of a bastioned front will be under 400
yards, while that of a polygonal front >¥ill be half as long again.
Hence the area that would be enclosed by twelve bastioned fronts
may be enclosed by eight polygonal fronts, the angles of the
polygons being respectively 150° and 135° To admit of com-
parison, these angles have been adopted for the fronts shown on
PI. V. From these it will be seen that^ although, owing to the
greater number of fronts, the angle of the polygon is larger by 15*^
for the bastioned fronts, yet that the salients of the bastions are
22° less than the salients of the straight polygonal fronts, while
these latter may be enlarged by breaking the fronts outwards.

In spite, therefore, of the longer exterior sides, which it must
be remembered are not necessarily adopted, a better fire can be
directed upon the capitals of the salients in the polygonal than in
the bastioned front ; and the faces furnishing this fire are less
exposed to enfilade, since enfilading batteries must be brought
nearer to the collateral fronts. With a greater length of crest line,
less of this line has to be sacrificed to traverses, and so a much
larger number of guns can be opposed to the besieger.

As regards the screening of the escarp, this, as has been shown,
requires narrow ditches. But guns on open flanks cannot be
placed at close intervals [as in casemates ; thick traverses are
needed ; and for the flanks of a bastion a length of 50 yards has
been usually thought necessary. The ditches of the bastions
cannot be greatly narrowed without some loss of the power of the
flank, and in any case the escarp of the curtain at the ends of
the tenaiile must be ill protected ; so that the obstacle to assault
is less to be relied on with a bastioned, than with a polygonal
trace.

The advantages of casemate flank defence, always provided that
the casemates are well covered from distant fire, have been already
mentioned. The open flanks of bastions are frequently exposed
to every kind of fire — frontal, enfilade, high angle, and reverse,
and the guns mounted on them disabled long before the besieger
reaches the coimterscarp. It has also been pointed out that the
tenaiile interferes with casemate flanking on a bastioned front. It
is true that casemates may be provided to flank the curtain, and
that caponiers may be placed at the salients o£ the bastions to give

1^4

PElSfANENT FORTIFICATION.

Advaatages of
the polygonal.

As applied to

irregular

ground.

OccasioDal
exception?.

Importance
of thebas-
tioned trace.

a reverse flanking fire along their faceB. But efficiency and economy
are alike opposed to a multiplication of special flanks — economy
of money in the original construction, and of men and guns in the
defence. The arrangements to guard against a danger which may
come at any moment, or may never come at all, should be
especially simple and sure. The pieces held in readiness for it
should be no more than arc strictly needful, and therefore the power
of each piece should be developed as fully as possible. The poly-
gonal trace in which, owing to the longer exterior sides, two
caponiers are the equivalent of six bastion flanks, has evidently
the advantage in these respects, apart from the superiority of
casemate flanking.

As regards, therefore, the effectiveness of the fire upon the
country, the preservation of the obstacle to assault, and its due
flank defence, the polygonal trace is generally to be preferred.
Good communications, retrenchments, and bombproof cover may
be accommodated to either trace ; but as regards outworks, the
longer fronts of the polygonal trace justify larger ravelins, which
can be better organized for defence, and the more obtuse salients
make it easier for the ravelins to intercept the prolongations of
polygonal fronts than those of the faces of bastions. On the other
hand the ravelins afford each other less support. Mine attacks are
more formidable to the polygonal trace as they threaten the flanking
works.

When it becomes a question of applying these traces to actual
ground, another marked defect of the bastioned trace shows itself*
Its several parts are so closely interdependent that to touch one
is to affect all. A short front means a weak profile, and a change
in the direction of a face involves a change in the power of a
flank. The application of the principle, already referred to, that
the line of the parapet need not strictly adhere to the line of the
ditch, does something to lessen the stringency of the trace ; but^
nevertheless, it will usually lend itself far less readily than the
polygonal trace, to irregular sites.

There will, however, be cases in which the ground may actually
reconmtiend a bastioned trace, and where the ditches are wet its
drawbacks are by no means so marked. These drawbacks are to
be recognised, not in order that the trace may once for all be set
aside, but that, wherever special circumstances may suggest its use>
they may be taken account of and as far as possible obviated.

Also it must be remembered that if the polygonal trace is likely
to be in the main the trace of the future, the bastioned trace haa
been the trace of the past, and that fortresses live long and change
little. For many years to come bastioned fortresses may be
attacked and defended in war, repaired and ameliorated in peace ;
and the principles of their construction should therefore be well
understood.

Accordingly in the two following chapters examples are given
of a bastioned and of a polygonal front, so that they may be
studied in deteil. The bastioned front has a dry ditch, the poly-
gonal front a wet ditch, so that in each case the trace is applied
under the conditions which present most difficulty.

. the bastiomed tbage. 165

Section 2. — The Bastioned Tkace.

Modem French System,

257. The bastioned trace, invented by Italian engineers in the
16th century, was carried by them all over Europe, and for more
than 200 years remained the leading type of permanent fortifica-
tion. In France it stood especially high^ having become identified
vrith the great name of .Vauban, and been embodied in numberless
fortresses. From time to time^ however^ opponents made them-
selves heard^ of whom Montalembert was the most considerable.
The principles of his ** polygonal fortification " were adopted by
the German engineers in the early part of the present century,
and soon afterwards in most other countries. But the French
engineers^ as a corjis, continued until within the last few years to
maintain the general superiority of the bastioned trace and of
parapet flank defence, and did their best to obviate the various
objections urged against it. Accordingly the fronts taught in the
French military schools^ which have successively borne the title
of the modem French system^ have been generally regarded as
the best examples of the bastioned trace. It is the latest of these,
the modifications of which are due chiefly to General Noizet^ that
is now to be described.

258. The general construction of the trace is adjusted to Ck)n8truction of
three elements of it — the length of the curtain, the length and ^g^Jwe^^
direction of the flanks, and the length of the lines of defence.

The length of the curtain is such as to allow of the complete
defence of its ditch with the reliefs adopted for the flanks. These
reliefs will be examined later. The length of curtain resulting
from them is 134 yards. It is considered desirable that the flanks
should be 50 yards long, so that they may receive an armament
superior to that of the enemy's counter-batteries on the glacis at
the salients of the bastions. If the flanks are traced at right
angles to the lines of defence, the defence of the curtains becomes
very oblique for artillery firing through embasures. It is there-
fore thought better to make them chords of arcs struck from the
shoulders of the adjacent bastions. Notwithstanding the im-
provements in firearms the limit of 280 yards is still retained
for the lines of defence, wherever there is no special reason for
extending it. These conditions for the curtain, flanks, and lines
of defence are found to be satisfied by constructing the front on
an exterior side of 394 yards (360 metres), and with a perpen-
dicular of one sixth. The lines of defence so obtained are
produced sufficiently far towards the rear to give the required
length of curtain, and the flanks are then drawn at the due angle,

which will be 99^°, viz. ^ — ^ + 18i°; the diminished angle,

with a perpendicular of ^, being 18^®. with the line of the
curtain. The length of the faces resulting from this con-
struction is very little short of one third of the exterior side, so
that the bastions are not inconveniently small. Their flanked
angles might sometimes be too much reduced ; but in that case.

166

PERMANENT POKTIFICATION.

Main ditch.

Tenaille.

RaTelin.

Traverse of
the ditch of the
ravelin.

Keep of the
ravelin.

High and low
&ce8 of the
ravelin.

as where special circumstances of ground affect the trace^ a com-
promise must be made among the determining conditions.

A width of 26 yards is given to the main ditch at the salients
of the bastions, and the counterscarp, rounded here, is directed
upon points in the superior crest of the flanks 5 yards inside of
the angles of the shoulder, in order that the whole ditch may be
as narrow as possible without sacrificing flank defence.

Owing to its low relief, the fire of the tenaille is not of much
value, while its occupation as an outwork requires that it should
be revetted on all sides. Accordingly, it is here constructed
solely with a view to its primary function of screening the escarp
of the curtain and flanks. It is, in fact, a simple traverse or mask,
5 yards thick at the top, and unrevetted except at the ends. It
runs parallel to the escarp of the curtain, from which its inner
crest is 20 yards distant. At 1 1 yards from the flanks the ends
are returned and carried forward parallel to the flanks up to the
lines of defence.

259. To obtain as much saliency as possible for the ravelin with-
out forfeiting effective flank defence from the bastions for its ditch
and glacis, its salient angle is made 60®, and its faces are directed
on points on the faces of the bastions 36 yards from the shoulders.
The width of its ditch is 17^ yards, or two thirds of the
minimum width of the main ditch. To prevent a breach being
made in the body of the place through this ditch the ends of this
opening are completely closed by traverses resting upon the
counterscarp of the bastions, and having a thickness at top of
6^ yards, with an exterior slope of ^. On account of these, the
faces of the ravelin are not produced up to the counterscarp of
the bastions, but are stopped at lines drawn parallel to this
counterscarp and 22 yards in front of it. From the extremities
of the faces, the line of the gorge runs at right angles to them
until it is 4 yards within the exterior side, when it becomes
parallel to that line.

Against the portions of the gorge-wall, which are perpendicular
to the faces, rest 'glacis-traverses to intercept the enemVs fire
along the ditches of the keep of the ravelin*

This keep, or r^duit, is a lunette ; its gorge is 70 yards long
and coincides with the exterior side, and the flanks are perpen-
dicular to the gorge so as to fire directly upon the enemy's
lodgments opposite the salients of the bastions. The length of these
flanks is 30 yards, which allows the traverses in the ditch to screen
not only the shoulders of the bastions, but also the gaps between the
bastions and the tenaille. The faces instead of being made
parallel to those of the ravelin, as in earlier systems, are drawn to
a point 88 yards in rear of the ravelin salient. By this con-
struction a better fire is brought to bear upon the enemy's
lodgments on the terreplein of the ravelin ; sorties are facilitated,
as there is room for an earth slope instead of a revetted counter-
scarp ; and the enemy's further approaches against the keep are
made longer and more difficult. At 120 yards from the salient
of the ravelin (measured along the escarp) the faces of that work

TH£ BASTIONED TRACE* 167

are abruptly dropped to within 4 feet of the level of the escarp.
The object of this construction is to give freer action to the flanks
of the keep^ and also to prevent the enemy driving out the
defenders 'from the keep of the re-entering place of arms by
working along the faces of the ravelin. At the extremities of the
high faces, and for a length of 20 yards from them^ the terreplein
has a retaining wall instead of an earthen slope.

260. The covered way has a minimum width of 1 1 yards, but to Covered way.
obviate enfilade the line of parapet is indented upon the branches
opposite the ravelin. The returns, or crotchets, are 7 yards long,
and are made perpendicular to the capital of the ravelin, so as to
bring a fire to bear upon an enemy advancing against the salient
of that work.

In the re-entering place of arms the crest lines are parallel to Re-entering
the counterscarp of the ravelin and bastion, and at distances from place of anns.
them of 55 yards and 66 yards respectively. Its junctions with
the branches of the covered way are closed by traverses, which Traverses,
are perpendicular to the counterscarp, and are made 16 yards
long, so that the passage round them may be thoroughly sheltered
from the enemy's view. There is also an advanced traverse in
each branch of the covered way of the ravelin shutting off the
salient place of arms ; but intermediate traverses are omitted,
because they mask the fire of the place and give shelter to the
besieger, interfere with the movement of the troops along the
covered way, and require a sacrifice of banquette.

The advanced traverse is so placed as not to mask in any degree
the fire from the opposite bastion. Accordingly the base of its
exterior slope is determined by a line drawn through the salient
of the ravelin and the inner extremity of the crest of the traverse
of the re-entering place of arms upon the opposite branch of the
covered way.

The faces of the keep of the re-entering place of arms are parallel Keep of re-
to those of the place of arms itself, the escarp line being 22 yards entering place
inside of these. The faces are bounded on one side by the coun- ° "™^*
terscarp of the bastion, on the other side by a line parallel to that
which determines the advanced traverse, but 4 yards in front of
it ; so leaving room for a roadway along the end of the keep under
cover of the rear traverse. The counterscarp, of the keep is un-
revetted. The bottom of the ditch is 4 yards wide and the ends
are sloped upward towards the bastion and ravelin respectively,
so that it may be thoroughly flanked throughout, and eo that it
may offer no gaps through which the escarps of the works in rear
might be reached. The keep itself is a casemated work, having a
width of 13 yards on each face. Its casemates open on an inner
court, 20 feet below its upper terreplein. To separate the terre-
plein of the keep from the traverse of the ravelin ditch, the latter
is dropped 4 feet for a length of 14 feet adjoining the keep, and
this also allows the fire of the bastion to search the interior of the
keep more thoroughly- In the opposite direction the traverse of Traverse of the
the ravelin-ditch is continued up to a line joining the end of the ^<»^^tlie
tenaille with the inner end of the low, face of the ravelin, so that it

168

PBBMANENT FOBTIFICATIOK.

Escarps.

Profile.

Reliefs.

CoTered way.

intercepts all shots across the ditch that might otherwise pass
through the gap between the tenaille and the bastion. From this
point the counterscarp of the bastion is returned and runs parallel
to the face of the ravelin up to its gorge.

261. In all the above works the escarps are demi-revetroents,
either solid or counter-arched. They may contain musketry
galleries or gun casemates, but these are looked upon as accidental
and subordinate^ and except in the case of the dead ground at the
ends of the tenaille, the defence of the ditch is nowhere dependent
on them.

As regards the profile of the several works, a thickness of
6^ yards is given to the parapets of the body of the place, of the
ravelin, and of its keep ; and a thickness of 5^ yards to the para-
pet of the keep of the re-entering place of arms. The parapet of
the low faces of the ravelin is 8 yards thick^ and has no exterior
slope. The exterior slope of the body of the place is ^ ; for other
parts of the system it is ^. The inner edge of the terreplein is in
the body of the place 14 yards; and in the ravelin and its keep
11 yards^ in rear of the crest (except where ramps occur). In all
of these and in the covered way the terreplein is 9 feet below the
crest of the parapet. In the keep of the re-entering place of
arms the inner edge of the terreplein is 5 yards behind, and 6^ ft.
below the crest.

262. The crest of the body of the place has a fall of 3 feet from
the salient to the shoulders of the bastions, and a further fall of
1 ft. 6 in. along the flanks ; the crest of the curtain is horizontal.
By this means the terrepleins are better defiladed from view, and
the salients have an increased command over the country. The
same principle is applied to the high faces of the ravelin and to
its keep. In each case the crest has a fall of 1 ft. 6 in. from the
salient to the inner extremities. It is necessary that the curtain
should have a command of at least 1 ft. 6 in. over the salient of
the keep of the ravelin, and this latter as much over the salient of
the ravelin. Hence the salient of the ravelin will be 7 ft. 6 in.
below the salients of the bastions. A command of 7 ft. is given to
the ravelin over the crest of its covered way, which is not too
much for the due defence of the covered way by musketry fire,
and at the same time allows the glacis to be swept by artillery
fire from the ravelin, without being made flatter than ^ As the
covered way of the ravelin is generally the first to be crowned by
the besieger, it is desirable that that of the bastion, and the re-
entering place of arms, should have a slight command over it ;
accordingly their crests are made 1 ft. 6 in. higher. The com-
mand, therefore, of the salient of the bastion over the crest of its
covered way is 13 feet, and the glacis may here have a slope of
^ without losing artillery defence. In order that the keep of
the re-entering place of arms may mask the fire of the works
behind it as little as possible, it has a command of only 2^ feet
over the crest of the place of arms, which is- no more than is abso-
lutely necessary to prevent its being looked into from the enemy's
lodgments.

THE BASTIONED TRACE. 169

The^ escarps ai^ sunk so that they tnay be screened^ not only Escarp,
from view, but to some extent from curved fire. On the faces of Body of the
the bastions their tops are on a level with the counterscarp, that P^®*
is to say, they are 9 feet below the crest of the covered way. As
the height given to the escarp is 33 ft,, this makes the total relief
of the salient of the bastion above the bottom of the main ditch
to^be 55 ft The relief of the inner extremities of the flanks
would therefore be 50 ft. 6 in. ; and if the main ditch were level
throughout, the length of the curtain necessary for its complete
defence would be 162 yards, instead of 134 yards. This, how-
ever, would inconveniently reduce the length of the faces of the
bastions, making them little more than one fourth of the exterior
side. Accordingly along the ends and rear of the tenaille the
bottom of the ditch is given a slight inclination upward towards
the middle of the curtain ; being in this part 7 ft., and at the
angles of the flank 3 ft., above its level in front of the faces of
the bastions. The top of the escarp is given a corresponding
slope along the flanks, so that the height of 33 ft. is maintained
for them ; but it is not thought necessary to incline it similarly
along the curtain, as escalade is least likely here, and 29 ft. of
escarp is thought sufficient. The sloping of the ditch is also
convenient for drainage. To drain the ditch in front of the
bastions it has a fall, both from escarp and counterscarp, towards
the middle, where there is a small cunette. To economise masonry
in the counterscarp, the level of the bottom of the ditch in this
side is about 10 ft. higher than on the side of the escarp.

263* The top of the escarp of the ravelin is on the same level Ravelin,
as that of the faces of the bastions, but the height of the escarp is
only 23 ft., the bottom of the ditch being 10 ft. above that of the
bastions. In this ditch there is also a cunette. The top of the Keep,
escarp of the keep of the ravelin is at the salient 3 ft. above that
of the ravelin, but it has a fall corresponding to that of the crest,
so that the extremities of the gorge are 1 ft. 6 in. lower. The
bottom of the ditch of the keep is similarly inclined, so that the
escarp has an uniform height of 16J ft. In the keep of the re- Keep of the
entering place of arms the top of the escarp is of the same level ««-«>»termg
as the extremities of the gorge of the keep of the ravelin ; the
height of the escarp is 13 ft. This height, however, is reduced
by the upward sloping of the inner ends of the ditches of the
keep ; and in these parts a parallel slope is given tq the top of
the escarp so as to maintain a height of not less than 1 1 ft The
same thing occurs with the inner ends of the escarp of the ravelin ;
but here a height of 14 ft. is maintained. The crest of the TraverBes
traverse closing the ditch of the ravelin is on a level with the
top of the escarp of the face of the bastion which it is meant to
protect. The inner crest of the tenaille is also at this level. Its
outer crest and the crest of the traverse closing the ditch of the
keep of the ravelin are 1^ ft. lower.

The assumed relief of the plane of site is 31 ft. 6 in. above the Plane of site,
bottom of the bastion ditch, which is in fact the same as the crest
last mentioned, and as the top of the counterscarp of the ravelin.

42642. M

arms.

170

PEBMAKBNT FOBTHIOATION.

Communioa-

tiODf.

Postern under
cartain.

Double
caponier.

If it were bigher tban this the command of the crest of &&
covered way would be insufficient ; if it were lower, the conil
paratively narrow ditches would not furnish earth enough for tU|
ramparts and glacis. '

264« The communications in this Bystem are so disposed tl
the road to and from one outwork shaU not lie through another]
as the inner work may be thereby compromised. Bamps are
almost all cases used instead of stairs, and a general width
4 yards is given to them. Those leading to the terreplein of th
body of the place are inclined at J or -^ ; but outside of thi
they are inclined at J. A postern 4 yards wide and inclined at
runs under the middle of the curtain, and opens upon the facet
its escarp 5 ft above the bottom of the ditch. The communicatioi
with the tenaille is either by a temporary wooden bridge at thii
level, or by descending by moveable steps into the ditch am
mounting again by ramps on the reverse slope of the tenaille
Another postern leads through the tenaille, falling 4 ft., and thaj
roadway issues therefiom 8 ft above the bottom of the ditch ofj
the bastions. At this level it passes across to the gorge of the^
ravelin, screened by a double caponier, of which the crests aref
9 ft. above it and 14 yards apart, and the superior slopes at such
an inclination that they may be swept by the artillery fire of the
flanks. This caponier may be discontinued at about 8 yards
from the gorge of the ravelin, as the roadway there comes under
shelter of the inner ends of the traverse of the ravelin ditch. This
sheltered space, widened by the 4 yards interval between th^orge
lines of the ravelin and its keep, which is kept at a level IJ ft.
higher, serves as a secure place of assembly for troops, and here
the several lines of communication separate. Kamps lead right
and left, between the gorge lines, into the ditch of the keep, and
thence up the counterscarp on to the terreplein of the ravelin.
Steps to keep. Flights of steps, 2 yards wide, along the gorge-line of the keep,

communicate with. its interior, which for better cover is kept, for
a width of 10 yards measured on the* capital, 16 ft. below the
terreplein at the salient, and then rises to this by a wide con-
vergent ramp inclined at ^. Lastly, the roads to the covered
way run along behind the gorge of the ravelin, and mount 7 ft.
by ramps into the returned ends or the counterscarp of the bastions.
Each of these then runs parallel to that counterscarp in front of
the traverse of the ravelin ditch, being. secured by a glacis on the
outer side, the crest of which is 8 ft above the road. Then it
again mounts about 12 ft. by a ramp along the end of the keep
of the re-entering place of arms and under cover pf the inner
traverse of the ravelin branch of the covered way ; and by another
ramp, on the counterscarp of the ditch of the redoubt, it gains the
remaining 6 ft up to the terreplein of the place of arms. To
prevent the enemy making use of these communications^ to
penetrate into the place, there is a gap or haha, 4 yards wide,
temporarily bridged over by planks, at the top of the ramp which
runs along the end of the re-entering place of arms. The com-
niiunication with the covered way, when the planks are removed,

1 » '

Bamps to
raTeha.

Ramps to
covered way.

Modern French

SYSTEM.

■:it<
m
l3e]
Id

isvi

* TMB BA8TI0NED TRACE. 171

18 by a postern running through the keep5 and opening into its
ditch about 20 yards from the counterscarp of the bastion^ having
a ramp 2 yards wide up the counterscarp opposite to it. The
communication with the ter^'eplein of the redoubt itself is by an
internal passage and staircase ; the entrance being from the inner
court, at the re-entering angle. Gaps similar to the one above
mentioned are made in the ramps behind the gorges of the ravelin
and of its keep. There is sallyport leading from the re-entering Sallyport,
place of arms on to the glacis of the bastion, and there is another
behind the advanced traverse of the covered way of the ravelin.

265. On comparing this system with those that have preceded General
it, as, for instance, with that shown on Fig. 1 of PL IX, the '^"""^
system of the school of M6ziSres,* it is obvious that some of the
chief defects commonly urged against them are here avoided.
That the escarp of the body of the place could be breached
through the ditches of the outworks before the crowning of the
covered way; that the communications were Intricate and unsuited
to an active defence, or to the recovery of works once captured ;
that the ravelin and its keep could be enfiladed from the same
battery, and that the main ditches were so wide as unnecessarily
to expose the escarps ; these objections are wholly, or partially,
obviated in this system. The escarps in this system are better
covered, while nevertheless their height is ample, and the
parapet flank defence of the main ditch complete (except at the
ends of the tenaille). There is much less dead ground in the out-
works where the enemy may find shelter from the fire of the
body of the place. The communications are not only simpler
but safer, and less compromising to the outworks. At the same
time masonry is economised, wherever, as in the coupure and
tenaille, the gain to the defence ia not commensurate with the
cost. The faults which remain are chiefly those which are
inherent in the bastioned method of fortification, and which have
been stated in the last section. It may perhaps he said that these
are unnecessarily aggravated by adherence to the old limits for
the lines of 'defence. But the great increase in the power of
artillery of late years has had to be met by a great extension of
the works of all the most important fortresses ; and in consequence
of this the continuous encein€es to which long fronts are especially
applicable have been largely superseded, at all events as the main
defensive line, by chains of detached forts which hardly ever
admit of them. A much more important point, looking to the
exigencies of such works as these, is the interdependence of trace
and profile In the bastioned method, which makes a strong profile
incompatible with a short front. Though something has been
done, as mentioned above, to shelter the escarps from curved fire
in this system, much more seems to be needed. The height of
the escarp of the body of the place would, no doubt, bear

* The ficole da g^nie was establiBhed at M^zUres from 1749 to 1793, when it was
transferred to Metz. The front elaborated and taught at M^zidres was long knoWA
as the modem French system.

M 2

172 PEBMANENT FOBTIFIGATIOK.

reduction, so that the top of it might be lowered without
increasing the reliefs. But with short fronts it becomes necessary
to decrease the reliefs, while, nevertheless, a sufficient commiand
over the country must be maintained ; and ^he escarps must then
become exposed. The difficulty has recently led some French
engineers to advocate a twofold front, — a low bastioned trace for
close defence, and behind this a higher line of rampart, not
necessarily broken into bastions, for good command over the
country and defilade of the interior. Fort St. Julien at Metz
was an example of this construction.

•

Section 3. — Polygonai, Trace — Antwerp Enceinte.

266. The front now to be described, as an example of the
polygonal trace, is a front of the new enceinte of the fortress of
Antwerp. Some account of that fortress, and of the strategic
part it is intended to play, will be found in the next section.
Owing to the importance of this part, the fronts of the enceinte
that are most exposed to attack have been fortified on a scale
which is usually forbidden by economical considerations, and at
! the same time with an originality and skill which makes them

especially worthy of study. Also, as the site is nearly level they
afford a general type with much less modification than is usually
needed.*

General des- 267. On account of the site, the main ditch is wet ; It is

cription. unusually wide, and is flanked by a very powerful central caponier.

The half fronts defended by this caponier are termed the faces.
The head of the caponier is itself defended by two jfirst fianksy
which, in order that they may be concealed as much as possible
from the enemy's view, are retired, and protected by orillons at
I the inner ends of the faces. The curtain joining the first flanks

I is broken into two half curtains, which are separated by a

defensible barrack constituted as a cavalier and retrenchment. To
protect this barrack two wings are added to the caponier. The
caponier is separated from the barrack by a low terreplein and a
J narrow ditch, and these, are defended by two second flanks, placed

f between the first flanks and the orillons. Immediately behind

I each orillon, and below ^the flanks, is a place if assembly for

' troops.

The caponier is covered by a counterguard, which is composed
of two branches^ and has a loopholed counterscarp gallery, from
which countermine galleries i*adiute. In front of this again is a
ravelin also composed of two branches, each made up of two
crotchets, and a casemated reverse battery. The ditch of the
ravelin is flanked by casemated low batteries, which also serve as
keeps to the re-entering places of arms.

* The following description has been drawn chiefly from ** La Fortification
Polygonale,*' by General Brialmont, the designer of Antwerp (Brussels, 1869), in
which fhe wholo scheme of defence, and the vaiious detttls of it, ai« stated and
discussed.

POLT60NAL TBAO£-**ANTWEBP ENCEINTE. 173

268. The construction of the trace is as follows : — CoDttmetioD.

The exterior side AB may be taken as 1,100 yards* B^ciih^

Through the middle point C, draw the perpendicular D C P, ^^^
making C D 104 yards, and C P 71 yards. D will be the salient
of the caponier.

Through P draw PQ parallel to the exterior side and 125
yards long. Q marks the outer extremity of the half curtain.

From Q draw the first flank QB, 34^ yards long, perpendicular
to Q D. Draw B O, perpendicular to the exterior side, and on it
set o£F B S, 12 yards long, for the second flank.

From V, 8 yards from Q on the line QP, draw V G'' perpendi-
cular, to the exterior side. On this set oflF G'' G' equal to ^ G G'',
and join G 6^ for the face of the orillou. To complete the trace of
the orillon draw I>K from the salient D, directed on a point in
B Q 3 yards from B ; and draw S K parallel to the exterior side.
The end of the orillon is given*, by a line paraUel to G^V and
4 yards from it, cutting D K in L.

The faces forming the head of the caponier are given by the Caponkr.
lines D Q. The caponier has an inner court whidh extends 22
yards behind, and 55 yards in front of the exterior side ; its width
is 11 yards at the front, increasing to 17^ yards at the rear. The
magistral of the flank is parallel to the- side of the courtyard and
33 yards from it. Thus it makes with the exterior side an angle
of 93°.

To trace the wing of the caponier, join G' with C, the point of
intersection of the pei-pendicular of the front with the inner end of
the courtyard, and draw a line parallel toD Q and 6^ yards inside
of it. The extremity of the wing O O' is found by drawing a
perpendicular to the exterior side from a point in Q P, 27 yards
from Q, cutting Q D in O' ; and the point O is the intersection
of this perpendicular with a line drawn from the middle of the
second flank, B S, parallel to Q P.

In order that the head of the defensible barrack may be com- Defensible
pletely protected by the wings, it is not carried beyond U, a point ijar^ck.
on P Q 9 yards short of the line L O, which passes through the
extremities of the orillon and of the wing. The flanks of the
barrack are about 84 yards long, and make angles of 100^ with
the head.

The counterscarp opposite the head of the caponier is revetted, Oativodob
and is carried parallel to the faces of the caponier and 20 yards
from them, until it intersects the line D G.

The salient of the counterguard E is 180 yards in front of the
exterior side, and the branches are directed on points H, 190 yards

from C.

The salient of the ravelin, F, is 295 yards in front of the
extcMor side, and the branches are directed on points I, 245 yards
from C.

* It actually varies from about 1,000 to 1,150 yards qn the Antwerp fronts. It
should be observed that the origioal dimensions are in moires, and, to avoid fraetionsi
they have not been in all cases strictly rcnderedi

174

pbbmanhkt fobshfioatiok.

Olwtade.

Ck)iPinaiidg.

Cavalien.

Orgsniflatioii
ofxBmparts.

I'he width of the main ditoh is 88 yards at the Balient and 55
yards opposite the oriUons. The ditch of the ravelin is 66 yards
at the salient and 55 yards at the low batteries. These batteries
are traced at an angle of 115^ with the branches of the ravelin^
from points 48 yards from the intersection of these branches with
the counterscarp of the main ditch. A line drawn parallel to the
front of the battery aod 19 yards behind it marks the rear of the
gun casemates, and this line if produced gives the Jimit of the
ramparts of the ravelin and counterguard.

The minor details of the trace will be readily understood from
the plate.

269. With the excepticm of the head of the caponier^ the
defensible barrack, and the half curtains, the escarps and counter-
scarps are nnrevetted. The wet ditches are the obstacles to be
overcome, and these are widened at the salients, because the
^emy would probably endeavour to cross there. The depth of
wuter is about 10 feet, and the surface of the water is about
6 ieet below the plane of site. The escarps and counterscarps
have a slope of |. There is a berm, 16 feet wide, for the body of
thetplace, and 6 feet wide for the ravelin.

270. The conmiand of the body of the place over the country
is 33 ieet near the salients, 31 feet 6 inches at the inner ends of
the ffltces and upon the half curtains. The command of the ravelin
is not more than 15 feet, and that of the counterguard not more
than 21 feet ; consequently the outworks do not obstruct the fire of
the central part of the front, as is usually the case {e.g. in the
nSbdem French system), and the besieger is exposed to a plunging
fifir^ in his nearer approaches.

To increase this exposure, cavaliers with a command of 49 feet
are- made at the salients (on some of the fronts). They have
facesvand flanks, each about 48 yards long, measured on the crest
line ; the flanks making angles of 140° with the faces. These
plunge, down 'upon the besieger's lodgments and batteries, and
help tO; oppose his passage of the ditch of the ravelin, and his
establishment iif that work ; at the same time they form very high
traverses, protecting the faces from enfilade where it might other-
wis^e be possible.

On the top of the defensible barrack there is also a cavalier

'l)attery having a dommand of 41 feet, of which the flanks sweep

the ramparts and take in reverse the besieger's lodgments opposite

the ravelins of the collateral fronts, while the head directly

opposes the advance upon the capital of its own front.

271. The parapets are made 27 feet thick with superior slopes
of ^, and exterior slopes of |. The terreplein of the body of the
place is 66 feet wide, so as to leave room for continuous gun-banks
with a 30 feet roadway in rear of them. Shallow embrasures are
made for flanking guns, but elsewhere barbette fire is adopted.
The guns are either mounted on high carriages which will fire
over a 5 feet parapet, or they are field aruns which can be quickly
run down from the gun-banl^s and shifted from place to place,

POLYCK)NAii TBAdB — ^AKTWBKP ENCEINTE. 175

Hollow trayerBes are provided to shelter tfaexn^ and large bonnettes^
3 feet high, are made on the parapet to give protection against
ohliqne fire.

llie ramps leading up to the terreplein £rom the interior of
the place are nnusually wide, 26 feet for the body of the place,
and 18 feet for the outworks*

272. The height of the rampart of the body of the place gives Bomb-proof
unusually good cover behind it, and makes it easy to coDstruct ^^®'*'
secure blindages there for the troops held in readiness against an
assault. There are casemates for troops behind the escarp of the
half-curtains, and the defensible barrack is capable of containing

2,000 men in time of siege. The head of this barrack, however,
is not unlikely to be breached by indirect fire, as its front wall
rises to the fiill height of the crest line of the wings of the
caponier which are intended to screen it, but which are 120 feet
distant. It would probably be necessary, therefore, in case of a
fdege, to fill up the front portions of the casemates of the head.
(y. Fig. 2, PI. XI.)

273. The defensible barracks, besides acting as keeps and ^^^>^cl^meiit8.
guarding the main entrances, will also serve to flank a stockade

or wall, which may be Carried along behind the ramparts as a
retrenchment in case the enemy effects the passage of the main
ditch.

274. The first flanks of the body of the place have each a First flanks.
double tier of guns. The upper tier is on the main terreplein.

The lower tier consists of six guns in Haxo casemates. The
floor of these casemates is 6 feet above the water level. They
are about 13 feet wide with piers 3 feet thick, and at the outer
end is a passage leading into the place of assembly. These
flanks are intended, as already mentioned, to defend the head
of the caponier, and great stress is laid upon the completeness of
their concealment &om the enemy's view, as being the main point
of superiority of the Antwerp fronts, as compared with othtr
polygonal fronts. They can be seen only from the terreplein c)f
the counterguard, and it is assumed that the concentration of fire
upon this would make it impossible for the besieger to make
counter-batteries here.

The second flanks also have a double tier of guns, with two Second flanks,
guns in each tier ; but the front walls of the casemates are not
masked with earth as they are completely protected by the
orillons. The floor of these casemates is 8 feet above the floor of
the casemates of the first flanks,, in order that they may fire over
the merlons protecting the casemates of the first flanks, and that
they may not fire into each other.

The revetment walls of the orillons are built with arched Shelters und«r
recesses in which troops in the places of assembly can take shelter. ^^*^ orillons.
These troops are to guard the berm and to make sorties upon thj
besieger when he reaches it.

' 275. The caponier has in each flank 16 guns in cssematesi, aricj C;:ponier,
§}x, guns in open ba(,tery above. Of the tcMrrner, boweVer, onl^

176

PERMANEKT I'OBTIFIOATION.

Casematef*

eight gons would ordinarily be ready for action^ for, to give 6uf«-
ficient substance to the earth merlons covering the front walls,
alternate embrasures are filled up. If an embrasure is injured it
can be closed and its neighbour opened ; or if it is necessary to
crush a counter-battery at the salient all can be opened at once.
Such a counter-battery would, therefore, be directly opposed by
about 20 guns, and at the same time be taken obliquely and in
flank by 20 more from the neighbouring caponier. The two most
advanced casemates do not bear on the position of the besieger's
counter-battery. They are screened from this by the end of the
counter-guard, in order that they may be reserved to ^ve a reverse
fire upon the faces wheh the enemy's troops are mounting the
exterior slope.

The casemates are about 13 feet wide, with piers 3 feet thick.
Their floor is 3 feet above the water level They are 66 feet long
(v. Profile, Fig. 3), and can therefore serve as quarters for the
men required for the service of the guns. They were built with,
large openings at the rear into the courtyard, which would assist
ventilation, and would admit of mortar fire across the courtyard
and over the opposite flank ; but it has become necessary to block
up these openings almost entirely, to guard against splinters of
shells fired at high angles, and to prevent shells that may enter
through the ports of one flank taking the opposite flank in
reverse (v. dotted line).

The parapet of the open battery has a command of about 3 feet
over that of the counter-guard, and is provided with traverses,
about 24 feet wide and 48 feet apart, to lessen its exposure to
enfilade.

The parapet of the wings, besides its main function of hiding
the masonry of the defensible barrack, adds to the fire that can be
brought to bear upon the terreplein of the counter-guard.

The difficulty that the besieger would have in making counter-
batteries there, will, it is assumed, drive him to attack the caponier
by mining. To guard against this, there are counter-mines under
the terreplein of the counter-guard, and the revetment of the head
of the caponier is formed with three tiers of counter-arches filled
with earth, so that it may be difficult to breach, whether by mine
or by artillery.

Counter-gnatcL 276. The counter-guard acts as a keep to the ravelin, but its main

purpose is to cover the caponier, the half curtains and first flanks,
and the communications across the ditch. In its absence, the
enemy when established at the salient of the ravelin would be
able to breach the head of the caponier, to silence the first flanks,
and to make sorties impossible. Its salient is prepared for a
howitzer battery, to shell the besieger's approaches on the capital
It has an exterior slope of {, down to the dry ditch which separates
it from the ravelin, and at the base of this it is intended that there
should be a low wall or palisade as an obstacle.

277. The principle of the " independence of parapets " has been
freely applied in the trace of the branches of the ravelin. Owing
to this, and to the earthen roof of the reverse battery, which formi

Upper terre-
plein.

Wings.

Head.

Bavelin*

ENCEINTE OF ANTWERP

P. F. XI

Fig J.

Section on A B

+ 4-1

r Section on C D Defensible Barrcuk.

+ 23-5

Section on E F Caponier.

w o

30 ^ 4C
(400)

50 60

aoTeet

Ojyp.boj>ougol7e

Dan^rfifeld.Lith.22. Bedford Si Covent Garden

POLYGONAL TBAOE— ANTWEKP ENCEINTE. 177

a traverse 11 feet higher than the crest, the branches can be less
easily enfiladaded thati usual, and at the same time good frontal
fire is obtained upon the capital of the ravelin. The reverse
battery has four gun casemates on each side. They are especially
intended to make it impossible for the besieger, without waiting
to make himself master of the ravelins, to advance between them
up to the salients of the body of the place ; and when a ravelin is
itself attacked, the reverse batteries of the collateral ravelins
afford it valuable support. The earth mask at the head of the
battery protects it against fire from the front.

The low batteries of the ravelin consist of eix gun casemates Low batteries
with magazines and guard rooms. Their floor is 1 foot 6 inches, of the ravelin.
and the top of the earth cover over the arches 17 feet above the
water level of the ditch. They are kept as low as possible in
order that they may the less obstruct the flanking fire from the
rampart of the body of the place, and may be the less exposed
themselves to the besieger's fire. The inner half of the length of
the ditch is, however, necessarily bidden by them from the body
of the place, and they themselves are liable to be breached, not
only from batteries opposite the salient of the ravelin, but by
indirect fire from a distance. To preserve them for a time it is
proposed not to open embrasures in the covering parapet until the
besieger has brought his approaches up to the foot of the glacis ;
and the possible necessity of armour-plating them has been kept
in view, and prepared for. The batteries are enclosed in rear by
a loopholed wall, to secure them against assault, and to protect
the men in them from the case-fire of the caponier flanking the
counterscarp.

278. The covered way in front of the body of the place is Covered way
22 yards wide. In front of the ravelin it is from 9 to 15 yards and places of
wide, being made in crotchets to avoid enfilade. The length of the *""*•
short branch of the crotchets is limited to about 6 yards, so that it

may not give room for the besieger to place guns there to breach
tlie low batteries. Traverses are for the most part omitted as
obstructing the fire and the movements of the defenders, but a
long traverse is carried across the re-entering place of arms, in
order that the communications with the covered way of the faces
may not be exposed to the besieger's fire, when he is established at
the salient, of the covered way of the ravelin. There is also a
traverse at this salient, and behind this traverse, as well as behind
the traveri^es in the re-entering place of arms, it is intended that
blockhouses should be made immediately before a siege, to give
shelter to the guards posted in the covered way, and to some
light field guns or mitrailleuses for which gun-banks are provided.

279. On each front there are two main roads leading out of Commmiioa-]
the place. Each of these passes through an arched gateway *^®°®JJJ**^*^®
under the half-curtain, and across a bridge on to a causeway at

the end of the wing of the caponier. Another bridge and a
longer causeway carries it across the main ditch, and it then runs
along tlie counterscarp. Behind the low battery flanking the
ditch of the raveUn, it crosses by another bridge into the re*^

178

PBBMANBIIT FOBTIVIGATIOll*

Commimica<
tions with
cAponkr.

General re-
marks on the
front.

entering place of anns, and isflues out Into the oonntry by S/ cot
through the gUicis. Its width k nowhere loM than about 9
yardf, so as to allow troope to march out in colunm of Bectiona
The inner ends of the bridges are moveable, and are made in two
halves, to give the desired width of roadway, and to allow of the
repair of one half without interrupting the communication.
Boiling bridges have been used in most cases, but behind the low
batteries of uie ravelin drop bridges have been adopted, in order
that the communication may be more instantaneously cut off.

In addition to the. main gateways there is a passage, 9 yards
wide, on each side of the defensible barrack, separating it from the
half curtains. This passage leads by a bridge on to the low
terreplein in rear of the caponier, and from this there are poBtems
leading into the casemates of the flanks, and into the central eourt.
Passing through the central court there are other posterns at its
outer end connected with bribes across the ditch of the caponier.
These bridges would be destroyed, and the posterns closed, as soon
as the besieger is near enough to make assault or surprise possible.
Staircases lead from the low terreplein to the upper terreplein of
the caponier and its wings, and if the main gateways are destroyed
by the besieger's indirect fire, accese; to the causeways in front
of them may be had by means of temporary bridges thrown across
from the low terreplein. The revetment of the extremities of the
wings is high enough to prevent their being scaled from the
causeways without ladders.

280. The main communications throughout are practically
level and very direct, generally well protected from the enemy's
fire, and convenient for sorties in force. The causeways are so little
above the surface of the water that they do not obstruct the flank
defence of the ditches, while they are themselves well swept by
the flanking batteries. They correspond to the general duuracter
of the design, which implies throughout a strong garrison, a
very powerful armament, and an active defence. The conditions
of th^ Antwerp enceinte are in many respects exceptional. It
is rare to be able to combine such long exterior sides with salients
so obtuse, and it is rare to be able to spend, so largely on the
fortification of an interior line of defence, and to be able to count
upon so large a garrison. But apart from the favourable cir-
cumstances of the case, it is important to note the skilful dispo-
sitions made to secure the advantages, without the disadvantages,
of a low site and a wet ditch. The utmost is made of this ditch
as an obstacle to the enemy, but great care is taken that it shall
not correspondingly hinder assumptions of the offensive on the
part of the garrison. The width of a wet ditch affords room for
powerful flanks, but the want of depth below tlie surface of the
ground makes it difficult to secure these flanks, if casemated,
against destruction by the besieger's distant batteries. Ob this
front, equal pains are taken to develop to the full the power of
the flanks, and to protect them as far as possible from injury.

The low batteries of the ravelin are the only exception to this^
and it seems to admit of question whether, obstructing as they do

p. F. XII

cb Magagm&s
b Sheifl Stores
c Gurv Rooms
ci BarrxLok/ Rooms

e. Gvuxrd' Roams .

f. BloMtouses

Oppzto-pa^

Dangerfield.Lith.22. Bedlbrd S^ Coveni Garden.

• ■ J ♦

v\\<\ vA'\ BIOV.

\ \\\'

<« «

V\k

FOBTBES8ES AKD 70BTS. 179

the fire of the body of the place, while their own fire can be
Rilenced without much difficulty, they are of any real advantage
to the front. They cover the communication with the covered
way, and serve as keeps for the re-entering places of arms, but
these functions do not involve the gun casemates and the con-
sequent dead angle. However, it is supposed that the reverse
battery at the salient would under any circumstances deter the
besiegers from attempting to pass the ditch near its inner ends.

There are other parts which it would now be desirable to
modify, in view of the progress made by artillery during the last
ten years, especially the ill- protected escarps of the defensible
barrack and the half-curtains, and the position of the main gate-
ways. But such changes would not affect any of the chief features
of the front.*

Section 4. — Fortresses and Forts.

281. Most existing fortresses were originally fortified for local, origin of
rather than for national objects. All towns as they grew to fortresses,
importance provided themselves with walls, to secure their wealth ^^ defence,
and liberties against their neighbours. When artillery began to

show its power at the end of the fifteenth century, many of these
towns, remaining unchanged, gradually lost the character of strong
places ; while others, richer or more threatened, made hnste to add
earthen ramparts \o their walls, so as to resist, and to make use
cfy the new weapon.

But with the progress of artillery, and to a great extent in National
consequence of it, the power of kings grew and that of their vassals ^^'^^^•
declined ; wars became more national, and frontier districts were
usually the scene, and their annexation the object of them.
Owing to this, fortification passed by degrees into the hands of the
general government The strengthening and maintenance of
important places was superintended by the king's engineers, acd
charged upon the finances of the state, and their relation to one
another, and to strategy, offensive and defensive, began to be more
distinctly recognised.

282. This change became plainly marked in the time of Vauban's
Louis XIV. In 1678, Vauban was charged with the preparation ^®?|^^^®*
of a general scheme of defence for the north-east frontier of France, ^ **^'
newly extended by the treaty of Nimeguen. He ])roposed that
between the Meuse and the sea, a distance of 120 miles, there

should be two lines of fortresses, with 13 places in each line.
When these lines had been completed by the construction of a few
new fortresses, nil the old fortresses further inland might he
dismantled, for he considered that France had too many of them.
There were in fact, a few years later (in 1706) 119 fortresses and
178 minor posts in France, their aggregate peace garrisons

^^^^^^■•i^B^B^P^^.— ^-»^^.^.""^~^'^"~^— ^^^™^^^^^~^^^^^'"^"~" —^^^-^^.^Wi^^B^— ^— — B—^^^— ^^^m^^m^^^^^

♦ General BriaUnont gives (Fortification Polygonale, chapter 8) an amended front,
showing yarioils minor fUterations that he would be disposed to make. The position
pf the gatieways was due to civil requirements.

180 PBR114NEKT TOBTiriCATION,

amounting to 150^000 men. In creating his frontier lines, he did
not confine himself^to the construction or improvement of fortresses.
He paid particular attention to the roads and canals which might
be made of service to armies operating on the defensive between
these places. Roads perjpendicular to the frontier were barred by
them ; and, in rear of them, new roads and canals were made
parallel to the frontier, forming at once lines of obstacle and of
communication.

The value of this barrier was soon put to the proof by
Marlborough's victories in the Low Countries. " At the time of
the reverses of Louis XI V.,** said Napoleon,* *'this system of
" foitresses eaved the capital. Prince Eugene of Savoy lost a
** campaign in taking Lille ; the siege of Landrecies gave Yillars
'^ an opportunity of changing the fortune of the war : a hundred
" years afterwards, at the time of Dumouriez's treachery, the
*' fortresses of Flanders once more saved Paris ; the combined
'* forces lost a campaign in taking Conde, Valenciennes, Quesnoy,
" and Landrecies."
Deyelopment Throughout the eighteenth century the system of frontier lines
of thiB system. * of fortresses enjoyed a high reputation. Fortresses in the heart of

the country might, it was allowed, be necessary for weak states^
to serve as places of reiuge ; but for powerfnl nations it was better
that they should all be upon the frontier, to detain the enemy
there, while armies were getting ready to meet him. Also, places
in the interior might furnish the seditious with a handle to rebellion,
and give the king trouble to recover them ;t for the French civil
wars were not yet forgotten.

As methodised by Cormontaingne and D'Ar9on, each frontier
presenting no natural obstacles to invasion should be protected by
three lines of fortresses. The places of the first two lines were to
be placed chequerwise, so that those of the second line should bar
the intervals of the first; and these intervals between the places
in each line, and also between the lines themselves, were not to
exceed the length of a day's march, so that the garrisons might
attack convoys passing between them, without venturing too far
from their fortresses. The places of the third line, larger and less,
numerous, were to be grand dep6ts, and those of the second line
were to be entrepots, of war material. Between the fortresses,
armies could manoeuvre with their flanks secured — curtains, as
Guibert said, with the ))laces as their bastions; waiting their
opportunity to attack the invader when he became involved in a
siege.}

Experience of 288. During the wars of the Eepublic and Empire the
K^ ^w" ^ ^^* importance of frontier fortresses was repeatedly shown. For
Empire? *" instance, the Spanish fortresses on the frontier of Portugal —

Badajos, Ciudad Rodrigo, and Almeida — long hindered the

* Memoirs, dictated at St. Helena.

t Maigrety Traite de la suretc des Etats par le moyen defi Forteresses. Paris, 1 726.

X D'AryoD, Considerations militaires et politiques sur les Fortificationsi Parin,

1796i

FORTRSSSES AND FOBTB. 181

advance of the British army into Spain ; and San Sebastian and
Pampeluna delayed its passage of the Pyrenees.

But there were also many instances of an opposite kind,
especially in 18 L4 and 1815. The armies of the allies twice
pushed forward to Paris, unhindered by the 50 fortresses on the
frontier. Some of these promptly surrendered without being
formally attacked ; others were passed by the main armies, and
watched by corps little stronger than their garrisons. While
every man was needed for the forces in the field, and young
conscripts were fighting the battles which decided the fate of
the Empire, many thousands of veteran soldiers lay idle in distant
fortresses, exerting hardly any influence on the fortunes of the
war.*

These cases, coupled with the minor part played by sieges in
Napoleon's campaigns generally, led some writers to decry
fortresses altogether, and set sounder militiry critics to examine
their true use and value in the modern system of war.

As early as 1816, Rogniat, a distinguished French jijeneral of Opinions of
engineers, appealing to the experience of the two preceding years, ^fif"****
called in question the system of frontier lines of fortresses t
*' Are these pretended barriers, even if doubled or tripled, able
"to stop invading armies ? Does not the cost of their construc-
^' tion exhaust the wealth of the state for most uncertain results ?
'* Lastly, and this is the main point, may not the multiplied
'^ fortresses which the present system masses on the frontiers, be

for the most part more harmful than useful to the armies in the

field, by drawing off so many men for their garrisons?"
Unless they were placed actually within cannon shot of one
another, they would not prevent the enemy from marching between
them, and he need hardly leave a force equal to the total of their
garrisons to hold them in check. Meanwhile, the defensive army,
if driven back by some disasters into the interior of the country,
finds itself without depdts, arsenals, or points of support.

Instead, then, of massing the fortresses on the frontier, they
should be dispersed throughout the provinces that are Lkely to be
the theatre of war, to the very heart of the country ; they should
be large, s^ as to contain all that is needed for the service of
modern armies, and armies themselves should be able to take
shelter in intrenched camps under their guns.

Other writers of high authority supported his opinions. Jomioi.
JominiJ dwelt on the mischief of an excess of fortresses, and the
importance of their occupying strategic points and being of con-
siderable size. Small places, however, may sometimes be of value,
*' not to arrest the enemy, who will easily mask them, but to
" assist the operations of the army in the field ; the fort of
" Konigstein was as useful to the French in 1813 as the vast

* According to Colonel Vauvilliers (Nouvelles Considerations Militaires) there
-were 121,000 French troops in fortresses bejond the frontier, and an equal number
in French fortresses, in 1814.

Considerations sur TArt de la Guerre

See Brialmont, La Defense des £tats. Bmxelles, 1876.

182

1»ERMAKbNT rOHTlFlCATlON.

Aster.

Clausewitz.

Fortification
of capitals.

€(
it

€S

^^ fortress of Dresden, since it furnished a bridgehead on the Elbe.
^' In mountain districts small forts well placed are just as good
as fortresses, for all that is wanted is to bar the passes^ not to
provide a place of refuge for an army. The little fort Bard
came very near stopping the army of Bonaparte in the valley
of Aosta in 1800. Hence each part of the frontiers of a state
'* should comprise one or more great shelter fortresses, some
*' secondary places, and even small posts that will help the
** operations of the manoeuvring armies.'*

The same tendencies showed themselves in Germany. General
von Aster, who designed the new works of Ooblentz, and was one
of the founders of the new Prussian school of fortification,
insists strongly on the necessity oF basing all notions about
fortification upon the general principles of strategy and tactics.
At the points most suitalile for meeting and fighting the enemy
fortresses should be placed, which will assist the assembling of
armies, and give them shelter if beaten, and supply all their wants,
and which will oblige the enemy to divide his forces if he means
to pass by them. A fortress of this kind is " a veritable place of
'* arms, which is the thing required for the mode of warfare of
** the present day." Such fortresses may sometimes be placed
close to the frontier, but if they could be easily isolated by the
enemy it is better to retire them inland. It is a mistake to stud
the frontier with fortresses with the view of helping the offensive,
for ** if the offensive is successful they profit little, and if it fails
^ they are the more harmful, because they fall more easily into the
" enemy's hands than places further inland, and may perhaps
** help him to secure his conquests."* Small places are some-
times useful to bar passes or guard communications, but as
permanent works the cost of their construction and maintenance
is usually out of proportion to their value.

Von Clausewitz points out that two elements enter into the
eflScacy of a fortress : a passive element consisting of the shelter
which it affords to all that it contains, and an active element
consisting in its influence over the country round it As regards
the latter, it is not only more considerable, but its sphere is wider
in proportion as the fortress is larger, for the detachments s6nt out
to harass the enemy will be btronger, and can therefore venture to
a greater distance. Fortresses should tiot be entirely confined to
the frontiers. They are the *^ knots which hold together the
strategic web," and should be spread over the country, to assist
the defence of rivers and mountains, to furnish places of refuge
for defeated corps, to secure dep6ts and arsenals, and to protect
great towns, which are the natural storehouses of an army. The
capital itself should be fortified if circumstances will in any way
allow of it.t

As regards this last point. Napoleon's opinion was **that a

* Theoretical Survey of Permanent Fortification. 1828. (Uinterlassene Werke,
vol. 5.)
t On War. 1832. (Translated by Colonel Graham. London, 1879.)

FOBtBfiSS]^ ANt) FORTS. ) 83

• . - • ,

'* great capital is the native place of the flower of the nation^ the
^' central point of public opinion, the general depdt ; and that it is
^^ the greatest of all absurdities to leave so important a point
^' destitute of immediate defence.

284. During the reign of Louis Philippe, Paris was fortified ; JExpcrience of
and inadequate as its works had become when it was besieged in ^^^q^^ ^^
1870, owing to the rapid advance of artillery, its long resistance
and the heavy strain which it imposed upon the invading armies
sufficiently vindicated the wisdom of fortifying it. In several other
points the theories above noticed were illustrated, and for the most
part confirmed, by the experience of the last war. Metz and
Strasbourg lying close to the frontier were quickly isolated ; so
quickly in the case of the former, that the army resting on it
found its retreat cut off, and by its excessive numbers hastened
the fall of the fortress. Both places, when taken, helped the
invader to consolidate his conquests. The absence of any large
fortresses between them and the' capital, which might have arrested
the German advance and offered a second line of defence, was
very severely felt, and probably caused the disaster of Sedan. A
similar want hampered the armies raised in the west for the relief
of Paris. In the north the army of General Faidherbe rested on
the numerous fortresses of the Belgian frontier, and it was due to
these, cramped, antiquated, and ill-provided as most of them were,
that those raw troops held their ground so successfully. K the
fortresses had been fewer and better, the Germans, by their own
avowal, would have been greatly embarrassed.* Besan9on and
Belfort similarly supported the French levies in Burgundy, and
gave occupation to the corps of von Werder. Belfort, when
besieged, showed how vigorous a defence may be made by a
fortress capable of containing a strong garrison with widely
developed works. Toul showed how important a very small place
may become when it effectually bars an essential communication,
such as a main line of railway.

The case of Metz, however, i)roved that the principle of large
army-sheltering fortresses was itself capable of being pushed to a
disastrous excess. Napoleon, in criticism of Kogniat's proposals,
had said that an army of 100,000 men which allowed itself to be
shut up in an intrenched camp could be starved into suiTcnder
by another army, superior to it only by one third. But while the
successful blockade of Metz furnished a singularly exact confirma-
tion of. his opinion, its success was chiefly due to changes since his
day, which have made it possible to hold an extended position
with fewer troops, and to bring reinforcements more rapidly to the
point attacked, than could have been done then. Even now there
is a limit to such extension. An average of over 6,000 men per
mile was deemed necessary for the investment line round Metz,
27 miles long, and this could hardly under any circumstances be
safely reduced below 3,000. But the length of the investment
line depends on the fortress rather than on the troops inve:>ted, and

* y. Groetse, Operations da Corps da genie AUemaade, i. 276.

184

PERMANENT FOBTIPIOATION.

ClASsification
of fortresses.

Barrier places.

therefore a force of 60,000 men, instead of 130,000, in Metz, would
probably have needed 100,000 to blockade them effectually, and
would not have found themselves eo quickly starved out.

286. The various fortresses or permanent works which thus
appear to be needed for a complete system of national defence
may be grouped, according to their function, in two main classes,
depdt places and barrier places, the former having reference to
the supply, and the latter to the movements, of armies.
DepAt places. Depot places may be merely for the protection of magazines or

stores on the line of operations of an army; they may cover
arsenals and dockyards, in which war material is manufactured,
or large towns whose resources it is essential to secure ; or they
may further be required to serve as havens in which the national
forces, naval or military, may find shelter, and may be organised
and equipped.

Barrier places may guard mountain defiles, and they may control
railroads at points where, from th^ character of the country, it
would be very difficult to divert them. In either of these cases a
small fort will often be sufficient. But they are most largely
useful as bridge heads, giving command of both banks of a river
at points upon which main i*oads converge.

A single fortress, however, may serve at once as depot and
barrier ; it may contain a large city, be capable of sheltering an
army, form the knot of a network of railways, and occupy both
sides of an important river.

Such combinations of function are always to be sought for, in
order that fortresses may be few and powerful; and they are
usually to be found in the highest degree in the case of the
capital.

Places of this kind are the strategic pivots of a country, but
they may also play the part of tactical pivots, and support the
field army in a battle fought near them, either for their protection,
or for the sake of their assistance.

Combination
of functions.

Tactical nse of
fortresses.

Development
of the irorks.

Ontworks.

Outtcorks, advanced fVorks, and detached Works,

286. According to the position and importance of a place will
be the character and development of its works. It may consist
of a simple enceinte secure against assault, or this enceinte may
be strengthened to resist a regular siege by outworks, advanced
works, or detached works.

The outworks that are most frequently added have been already
described in the preceding sections of this chapter. Others are
often to be met with in old fortresses ; because, with weapons of
short range, the passage of the ditch and establishment in the
breach was usually the stage in the attack which could be most
obstinately and successfully opposed, and, therefore, to accumulate
outworks, each with its own ditch, was the best means to prolong
the defence. But in the present day they may be sources of
wer knees rather than of strength, giving a feeble fire themselves
while masking the fire of more important works behind them.

Jp-OllTItbSSfeS ANt) FOllTS. 185

and exposing the escarps of those works to be breached by the
besieger through the gaps afforded by their ditches.

To avoid this latter disadvantage, or . to gain greater saliency. Advanced
works may be thrown forward, and placed on or beyond the works,
glacis, sufficiently near to the enceinte, or its outworks, to be
defended by their rtiusketry fire. These are termed advanced
works. They are commonly lunettes or Jlickes, with slightly Lunettes,
closed gorges, and are usually placed on the capital of a bastion
or a ravelin, so that they intercept the besieger in his advance
upon the work they cover, or bring a flank fire to bear upon him
if his attack is directed on some other point. Plate XIII.,
representing a part of the fortress of Strasbourg, gives examples
of advanced lunettes (Nos. 52, 53).

It also shows another more capacious form of advanced work, Horn works
termed a hormoork, which was formerly touch used (Nos. 47, 49). and crown
The head is a bastioned front, and is therefore self-flanking, while
the sides or branches are flanked from the works in rear. If,
instead of a single bastioned front, the work has two bastioned
front«> it is called a crownwork ; and if three, a double crownwork
(v. F.F., PI. XLV).

287. When, as is now usually the case, the points outside the Detached
fortress which it is most important to occupy, do not admit, ^°'^^-
owing to the distance, or to the form of the ground, of the works

upon them being defended by the musketry fire of the place,
those works must be provided with their own flank defences on
all sides, and they then become detached works.

The employmeht of such works in special cases has always Example of
been necessary. The fortress of Badajos, besieged and taken by Badajos.
the British in 1812, affords instances of the use of them. Imme-
diately opposite to the castle of Badajos, and on the other bank of
the Guadiana, at a distance of 500 yards, are situated the heights
of San Cristoval, rising nearly as high as the castle. As the
terreplein or space of the castle sloped towards the Guadiana
every part of it was seen from those heights ; and to prevent a
besieger from readily availing himself of this circumstance, a fort,
had been constructed on them. On the south-east the heights of
San Miguel extend to within 500 yards of the place, and offer
favourable positions for batteries to breach the escarps of the
Trinidad and Santa Maria bastions, the glacis not being high
enough to cover them. It had therefore been occupied by Fort
Picurina, which the British were obliged to take before they
could carry on the projected attack against the place itself. On
the south-west side, a small crownwork, called the Pardaleras,
occupied some high ground about 300 yards from the place, and
defended the hollows beyond, which could not be seen from the
fortress. The lunette San Roque covered the bridge over the
Rivillas, and that over the Guadiana was protected by a small
homwork on the right bank.

288. But since 1815, detached works have, owing to several of detached
causes, received much wider application. The wars of the Empire, works.

as has been already shown, produced a general conviction that To allow of a
fortresses should be fewer and more powerful, so that in some ^x?"® *^^^®

42642. jf

186 PERMANENT FORTIFICATION.

caset} even an army might be received into them^ and take part in
their defence. At the same time it was necessary that, in the
absence of an army, such places should be capable of defence by a
moderate garrison. It was seen that the two requirements
would be best met by surrounding the fortress with a chain of
detached works, which would themselves need only small garrisons,
but would serve as pivots for troops operating freely in the
intervals between them.

Intrenched camps had been attached to several fortrcisses by
Vauban, who looked upon them as the surest means of hindering
a siege. But these were formed by continuous lines of field
profile, they lay on one side of the fortress, and were intended to
receive from 10,0C0 to 15,000 men. Chains of detached forts
had been propo:>ed by Montalembert in 1778 for the protection of
Cherbourg against bombardment or attack upon the land side.
Eogniat, combining the two ideas, recommended, in 1816, that
intrenched camps, capable of containing 100,000 men, should be
formed by means of detached forts placed about 3 miles apart,
and about 1^ mile from the fortress, and completely enveloping it.
The interval between two forts would form a field of battle,*
strengthened by field intrenchments, supported by the artillery of
the fortress, and perfectly secure on its flanks.

Detached works, though at much closer intervals, usually about
^ mile apart and ^ mile from the enceinte, were added by the German
engineers to their most important fortresses, such as Cologne,
Coblentz, and Verona,* and in fortifying Paris and Lyons the
French followed their example. The object at that time especially
aimed at, was to allow of a larger garrison, and of a more active
defence, and so to increase the difficulties of a regular elege.
To give But the introduction of rifled weapons gave fresh reason for the

bcw^^rdm*^^^* "®® ^^ detached works in order to provide against bombardment.

Especially in the case of dockyards, such as Portsmouth and
Plymouth, it became imperative to take up a new and very ex-
tended line of defence, which should keep the enemy at a distance
of about 5 miles from them ; and this could only be done by
means of a chain of forts.
To increase More lately, the experience of the war of 1870 has shown the

o^1[)k)ckade^ importance of a great development of the defences, in order to

prevent blockade by a comparatively small force. The perimeter

of the works at Paris was more than 30 miles when it was

besieged in 1870 ; but this has been considerably more than doubled

by the forts that have been since built, and one main object of the

extension is to stretch the investment line.

To lessen the That war showed also that, even with minor places, every effort

conver^nce of ghould be made to mitigate the convergence of the besieger's fire,

:9re. ^7 increasing the radius of the defensive works, and the long and

successful defence of Belfort was due to the energetic adoption of
this course.

* Their value had been strikingly shown in the defence of Colberg by Gneifienau,
in 1807.

FORTRESSES AND FORTS. 187

289. Strasburg has been taken above as an example of an old Antwerp,
fortress with multiplied outworks and advanced works. Antwei'p
may be taken as an example of a new fortress provided with
detached forts.

The system of frontier lines is even less applicable to a small System of
state like Bels^ium than to a more powerful countr\'. Its army, J*^l°"fi^V. ,

• II •/• 1 II • • 1 ri I X / ^ lence adopted.

especially ir weakened by numerous garrisons, is not Jikely to be
able to keep the field against the forces of its powerful neighbours,
and its best policy therefore is to concentrate all its means of
defence at some one important point, where it may hold out long,
and may receive assistance from friendly nations. Antwerp, the
commercial capital of Belgium, is best situated for the fulfilment
of these conditions. It is at a distance from the French and
German frontiers ; it fs covered by rivers offering good lines of
defence ; it has always abundant supplies of provisions and stores
of all kinds, and it has good communication with the sea. So
much of its neighbourhood can be inundated, that it cannot be
completely invested without a naval force, and can only be
regularly attacked on about one third of its circuit.

It was decided, therefore, in 1859, that Antwerp should be ^^dvancedlinc.
taken as the main pivot of the system of nntional defence, and that
the numerous frontier fortresses of Belgium should be suppressed.
But in order to give time, in case of a sudden invasion, for assem-
bling and organising all the forces of the country, and preparing
Antwerp for defence, Termonde and Diest have been retained, to
cover the flanks of the Belgian army while defending the line of
the upper Scheldt and its affluents, and delaying the advance of
the invaders. Driven back from this line, the whole army would
retire upon Antwerj), and its defences have therefore been designed
so as to form a, vast intrenched camp, capable of receiving
100,000 men, and affording them facilities for an active defence. -i

The old enceinte, which the town had long outgrown, has been Tbe enceinte i

demolished ; together with its famous citadel, built by the Duke of the fortress. f
of Alva in 1576. The new enceinte forms an irregular curved ^

line, about 9 miles in length, and consisting of eleven fronts. At
the north extremity is a citadel abutting on the river Scheldt.
{v. Plate .)

The seven southern fronts are alone exposed to regular attack.
Their normal type has been already described (section 3). Their
salients are in most cases very obtuse, so that the prolongations of
the fronts are intercepted by the ravelins, but the suburb of
Bcrchem made it necessary to throw forward the salient in advance
of it, and the fronts on either side of this salient arc therefore
provided with detached ravelins, and counterguards to the faces,
to protect the caponiers of these fronts from distant firC; and to
make it more difflcult for a besieger to establish himself at this
salient. This, and the two salients nearest to it, are also provided
with cavaliers.

The remaining four fronts, between Deume and the north
citadel, are of the simplest possible trace. They have a rampart

N 2

188 PEttMA?:ENT FOUTIFICATIOX.

and broad wet ditch, flanked by caponiers, having seren giins in ,
casemates on each side, but thej hare no ravelins.

The citadel. The citadel is a simple polygon of seven sides, varying from

350 to 500 yards in length, and has a broad wet ditch. The two
inner sides, facing the town, form a re-entering angle, ^nd defend
each other. The remaining faces are flanked by four caponiers
armed with artillery.

The citadel is intended primarily to allow the garrison to defend
the enceinte up to the last moment, and then to cover their retreat.
It is also meant to make them independent of the temper of the
population. Its position gives it the command of the Scheldt, both
beside and below the town ; so that it can protect the passage of
the gari'ison from the right to the left bank, when the enceinte
has Deen forced, and can also oppose vessels that may have passed
the lower batteries of the Scheldt.

The citadel and the four simple fronts adjoining it are provided
with a covered way and an advanced wet ditch, and they can be
further covered by an extensive inundation in case of attack*
The forts. In advance of this inundation, and extending from it to the

bank of the Scheldt above the city, is a chain of detached forts.
They are for the most part about 1^ miles apart, and from 2 to 3
miles in front of the enceinte. They are large and powerful
works, with a crest line of more than 700 yards on the front
faces, and about the same on the gorge side. Each has an arma-
ment of 120 guns and 15 mortars, and requires a garrison of 1,000
men. Their ditches are wet and are flanked by caponiers
mounting seven guns in each flank. In the gorge of each work
is a large casemated keep, screened by a glacis in front and a
redan in rear. It is assumed that the regular siege of one of
these forts would not be possible, in presence of the ^army en-
camped behind them, and that the enemy would attempt to carry
them by assault after a heavy bombardment. In the intervals
between the forts, batteries would be .thrown up and armed to
support them, as soon as the enemy showed where he intended
to attack.

On the left bank of the river there are other forts, existing or
projected, as shown on the plan ; and powerful batteries are to
be made at the bend of the Scheldt near Calloo for defence against
a naval attack. Small redoubts are also to be made on the dykes
to the north of the place^ lest gun boats of light draught should
avail themselves of the inundation to approach and bombard it.

Detached forts. 290. The size and relative position of detached forts will

depend on what is required of them. To give absolute security
against bombardment they must be four miles or more from the
place, so that ibr a complete circuit the length of the chain would
DC abbut 30 miles. If they are exposed to regular attack they

Their position, should not be more than 1^ miles apart, so as to suppoH; each

other eflfectually, and the form of the ground may often make it
necessary to place them nearer 5 but where it is etiough that they

Opp.po/ge iS8.

l^pt^KS.

should commaad the intervals between them, they may be placed,
in open country, 2 or even 3 miles apart.

The oize is mainly determined by the armament, and this must Their size,
be regulated in each case by the importance and the exposure of
the position, and the extent to which the fort can be supported
by its neighbours. AVider intervals will, therefore, demand more
powerful works ; but where the length of the chain is great, it
becomes very important that the forts should be no larger and no
closer than is absolutely needful> so as not to absorb an excessive
force for their garrisons. The usual allowance for each fort is
from 500 to 1,000 men, and from 25 to 50 guns for the armament
of the ramparts.

291. An example of a small detached fort, forming one of a Example,
chain surrounding a fortress, is given in Plate XV.

It is intended for an armanent of 24 guns on the ramparts, half
of them heavy guns (7 -inch or 64-pr3.), and a garrison of about
600 men.

The front is broken outwards sufficiently to let the prolongations
of the ditch pass near the adjacent forts, so that the enemy may
not be able to breach the salient caponier from a distance by firing
along the ditch.

In the case of a formal siege the fort would be supported, not
only by its neighbours, but by powerful intermediate batteries,
thrown up and armed as soon as the attack is foreseen. But to
give time for the construction of such batteries, it must itself be
able, in spite of the heavy convergent fire of the field guns, and of
guns of position, to arrest any advance of the enemy, and compel
him to bring up a siege train and to open trenches.

The most essential point, therefore, is a good organization of the
ramparts as an artillery position, combinmg freedom of action
with the utmost attainable security for the guns, the gunners, and
the ammunition.

The details will depend upon the way in which the guns are Organisation
mounted and the kind of fire for which they are intended. For of the ram-
high angle fire the terreplein may be 8 ft. below the crest of the ^^^^^'
parapet. But either the terreplein must be raised, or deep
embrasures must be made, to allow guns mounted on the service
carriages, or traversing platforms, to sweep the immediate fore-
ground. Deep embrasures are soon choked, and open barbettes
expose the gunners to musketry, so that where very wide lateral
range is not imperative, the compromise of a raised terreplein apd
shaUow embrasures is perhaps preferable to either.

Accordingly in this example gun-emplacements are provided on
the faces by pairs, one emplacement for direct and one for indirect
fire (the latter furnished with a musketry banquette); the
terrepleins for direct fire being only 6 ft below the crest, with a
loading trench along their front for the better protection of the
gunners, and with ramps allowing the guns to be quickly run
down under cover. Behind the gun terrepleins there is a sunken
way, 4 yards wide, and 12 ft, below the crest, for general circi]f|a'
tion along the ramparts.

190

PERMANENT POETIFICATION,

IVavenes.

Profile.

Caponiers.

Casemates.

Gorge.

Service of
ammuDition.

The several pairs of emplacements are separated by hollow
traverses serving as shelters for the lighter guns and for the men.
It is very desirable to keep the tops of these traverses level with
the crest of the parapet^ so that they may not help an enemy to
judge of the number and position of the guns of the fort But^
on the other hand^ with high terrepleins they give little pro-
tection against oblique fire unless they rise above the crest,
and the shelters in them must be sunk inconveniently low. It is
necessary to make a choice of the least of the two evils. They
are here, therefore, made only 3 ft. higher than the crest, in
order that they may be masked by a hedge on the exterior slope.
On the flanks there is still more reason for high traverses, in order
that they may give cover against highly curved enfilade fire, and
they are therefore shown here as 6 ft. above the crest, so as to
intercept shots descending at ^-. They are also prolonged to the
rear so as to give some protection against oblique reverse fire.
There is a traverse to each gun, but the emplacements are wide
enough to allow a second gun to be mounted if necessary. For
more complete protection the guns on the flanks may be blinded.
As regards the profile, a 15 ft. wall, if properly flanked, is a
sufficient obstacle ; but the top of it should be screened from the
enemy's fire, descending at J. The ditch is therefore made 18 ft.
deep and only 30 ft. wide, and the glacis is brought up to the
counterscarp. The ditch, with the interior excavations, will allow
a command of 24 ft. to be given to the crest of the fort.

The ditches are flanked by small one-floor caponiers, the heads
of which are guarded by counterscarp galleries, which at the same
time furnish a stating point for countermines. (See Fig. 5,
PI. XV. and PL XVI.).

The casemates for the men and stores are placed under the
rampart of the faces, and under the rampart of the gorge, and give
a total area of about 20,000 superficial feet.

The gorge is broken inwards parallel to the faces, so that its
ditches also may escape enfilade; and the central part of the
rampart is withdrawn from the escarp wall so that the gorge
casemates may open upon an inner yard. The consequent
narrowing of the work and reduction of the interior space is no
disadvantage, since, under the shell fire of rifled guns, the central
area becomes a place of more danger than the ramparts themselves,
and a bomb-proof passage across it must be provided for com-
munication from rear to front.

The ends of the gorge rampart become demi-bastions by this
retirement of the central part, and are able to furnish some flank
fire from the parapet to supplement the caponier. To protect
them from reverse fire one of the traverses of each flank is pro-
longed, so as to form a parados ; and this may be organized for
musketry, to serve as a retrenchment, or for high-angle fire.

Since it is not necessary to sink the escarp so low as upon the
front, the depth of the gorge ditch and the height of its rampart
are alike reduced.

Small cartridge stores for the immediate service of the ^uns are
placed in the traverses ; and alternating with them, on the faces.

-^=:^i^l^w^^yf*#jQ^wX -^?< i

li«ijmt«lt2?ltafi>rt.S'Co'Hi;Gna'

FORTRESSES AND FORTS. 191

there are cartridge lifts from the expense magazines. These^ with
the main magazines which are under the prolonged traverses of
the flanks^ are capable of containing more than 700 rounds per gun
of the armament of the ramparts. There are separate shell lifts^
and there are staircases also leading up into hollow traverses^ by
means of which the ramparts may be reached under cover.

Other i)oints will be sufficiently evident from the plate itself.

This example is given in order to show the grouping of the
several elements more readily and more plainly than can be done
by more general treatment ; but it should be well understood that
the details, almost without exception^ are open to modification^
not only to suit special features of site, but according to varieties
of armament, or the ideas of the individual designer.

292. In some of the works recently designed, the heavy guns in- Forts with
tended to oppose the besieger's batteries, instead of being mounted ^^^^^^
upon the front faces of the fort, are placed on an intermediate ^^'
rampart, lying between the faces and the gorge. The parapet of

this intermediate rampart not only protects the guns behind it^
but also serves as a parados to the troops manning the gorge
parapet, and will act as a retrenchment in case of assault. At the
same time it is kept sufficiently low to be screened from the
besieger's view by the parapet of the faces, so that he cannot mark
the eflfect of his shells upon it, and embrasures, if made in it,
present no target to him. The parapet of the faces is for the
most part intended for musketry and field artillery, to sweep the
foreground and repel an assault ; but at the salients there are
heavy guns on Moncrieff carriages.

293. Casemated keeps, or retrenchments^ are usually provided Keeps,
for the larger and more important forts of a line. They add
greatly to their security against assault, and to the chances of
driving out the enemy by a counter-attack; and they affi)rd
quarters for a part of the garrison. But it is necessary that they
should themselves be proof against aesault^ that their fire should

be able to sweep the whole interior of the fort, and that they
should not be liable to be breached or crippled by the indirect
fire of the besieger's batteries. In order that it may be the better
covered, a keep is sometimes completely enveloped by the rampart
of the fort, instead of forming part of the gorge. But in this case
it should be combined with a general retrenchment, so that the
troops holding it may not be deprived of all action upon the
ground outside the fort ; otherwise the besieger, when he has
gained the foi*t, will be able to push forward his attack upon the
enceinte of the fortress, without waiting for the capture of the
keep.

294. Citadels are the keeps of fortresses, supporting the garrison Citadels.
in standing an assault, covering their retreat, and imposing a
second siege upon the enemy. Where the population is hostile,

or where the gaiTison is insufficient for the extent of the place,
they may prove of great value. But by the development of
modern fortresses, the enceinte itself becomes, as it were, the

192 PKUMANKN'i' ITODTIFigATIOK.

citadel ; and though in special caseSj aa at Antwerpj eitadels may
still be built^ they belong mainly to the past.
Provisional 296. It will frequently happenj especidly in countries where per-

fortification, manent works have been sparingly provided, that when war is

imminent the great strategic importance of some points that are
not fortified will become apparent^ and they must be prepared for
defence within a few weeks' time. Or permanent works may be in
course of construction, and it may become necessary to complete
them hastily. Or, during the progress of hostilities, points may bo
occupied in the enemy's country, which it is essential to hold
securely with a small force. The term provisional is now com-
monly used to distinguish the character of the works constructed
in such cases, which is in fact a compromise between that of field
and that of permanent works, inclining to one or the other, aopord-
ing to the importance of the point, and the time and means
available.

In 1866 a very extended chain of works of this kind was
thrown up in seven weeks, around Florisdorf, on the north side of
the Danube, for the protection of Vienna, 7,000 men being em-
ployed daily. A litde later, when war had broken out, and the
Prussians had occupied Dresden, 6,000 labourers were sent there
from Berlin, and in a fortnight several detached forts and batteries
were built.

The leading distinction between provisional and permanent
works is the use of timber, rails, and T iron in place of masonry,
though the latter will not always be entirely excluded. Their
profile must usually be less considerable, and owing to the want
of depth in the ditches the flank defences will be le@8 well covered,
especially since timber caponiers can be breached at higher apgles
than masonry. Large use is, therefore, conunonly made of acces-
sory obstacles, abatis, wire entanglements, and mines, and the
flank defence of the ditch is sometiipes abandoned. In thp orga-
nisation of the rampapts, and the provision of blinded cover, they
will correspond generally to permanent works, in so far as may
be possible or necessary. They may eventually be converted
into permanent works, just as they may often gro^ out of ordinary
field works.

APFBNPIX A.

193

APPENDIX.

APPENDIX A.

Table of some of the principal Units of Linear Measure in terms of

English Feet, Yards, and Miles.

Locality. '

Unit.

—

Feet.

YardH.
-02880

Miles.

Remarks.

Austria -

Zoll (12 Linien)

•08640

j» " "

Fuss or Schuh -

1-03704

-34568

•

!» ~ "

Elle -

-85289

Klafter (6 Fuss)
Buthe (10 Fusb)
Meile -

2-0741
3-4568
5863-3

3-3312

» ■" ~

Meile (Geographisclie)

8100-8

4-60*iC

Bavaria -

Fuss -

-95751

-31917

•

Ruthe (10 Fuss)

3-1917

Berne -

Pied (12 pouces)
Aune -

•96216

-3-2072
-59557

>i ■ "

Perche

3-2064

Belgium -

Fuss (11 Zolle)
Elle -

-90466

-30155
-74845

Verge -
Meile -

4-9255
4860*833

2-7641

Denmark

Foot -

1-02975

-34325

Ell -

2-05950

-68650

England -

Inch -
Foot -

•08650
1 -.0000

-02777
•33333

Yard -

3-000

1-000'

7 F

• « * "

Ell -

1-250

%9 *

Fathom

^ ^

2-000

Pole or Perch -

5-500

3> * "
5J " "

Chain (100 links)

Furlong

Mile, common -

22-OOQ

220-000

1760-000

•125
1-000

?> * "

Ditto, Geographical
Nautical

2025-200

1-1506

r 60 miles =
\ 1 degree.

5J ■" *

League

5280-000

3-000

France t

Millimetre

„

•Q033

-0011

yy ^ *

Centimetre

-0327

•0109

•J " ™

Decimetre

-3279

-1093

New

•^ * *

Metre -

^•m

1-093G

* meai^ures.

jj ~ "

Kilometre

1093-63

-62138

Myriametre
Pouce (12 lignps)
Pied -

•08864
1-06571

10936-33

•02955
•35523

6-^138

Old

Toise (6 pieds)
Brasse Marine (5 pieds)

2*13142
1-77618

' measures.

Some of the measures given in these tahles are ohsolete, hut they have he^n retained so as.
to be available in working with old plans.
11 metres => 12 yards nearly.

194

APPENDIX A.

LocftUty.

Unit.

Feet.

Yards.

1
Miles.

Remarks.

France -
»» ~ "

LieuedePoste (2,0001

toises) - - J

Lieue Marine ( • 05 degre)

Mille Marine (-3331

lieue =1 minute - j

4262 84
6275 6
2025-2

3-4519
1-1506

( Same as Eng-
< lish nautical
(. mile.

Frankfort-on- 1
the -Maine J

Fuss -
Elle -

•9399
1-7703

•3133
-5901

Hamburg

»»

Fuss -
Elle -

•9399
1-8798

•3133
•6266

Holland .

Fuss - - -
Meile -

•9288

•3096
6404 12

3-6387

Naples -

Palma -

Canna - - -

•8628

•2876
2 • 3008

Persia -

Parasang

6299 04

3-579

Portugal -

Pie -

Palmo - - -

1 08266
•7171

•3608
•2390

Prussia -

»f ~ ~

»»

Fuss (12 Zoll.)

Elle -

Schritt

Klafter or Faden (6 Fuss)

Ruthe (12 Fu^s)

Mdle -

1^0297

•3432

•7293

•8234

2 0594

4-1188

8272-

4-7

fThe Ruthe is
divided into
tenths and
hundredths
lor survey-

L ing,&c.

Rome

Pi^de - - , -
Foot -

•9665
1

•3222

Russia -

Archine

Sachine (fathom)
Verst (500 sachines) -

•7777
2-3332
1166-6

•6628

Saxony -

Fuss - - -
Meile - - -

•9294

•3098
9923-326

6 6382

•

Spain

>» ~ *

Pulgado

Palmo - - -
Pie (Castilian) (12 Pul.)
Vara (3 Pies) -

•0761
•6849
-9132

•0254
•2283
•3044
•9132

Sweden -

Foot (10 inches)
Alner - - -
Mile -

-974
1-948

•3246
•6493
11688-

6-6412

Turin -

Pi^de -

Auna - - -

Pertica

1-1237
1-9714

•37458
•65714
6^742

•

Tuscany -

Pi^e (Geographical) -
Ditto (common)

1-9094
1-7985

•6364
•5995

Venice -

Pi^de -

Auna - - -

1-1410
2-0892

•3803
-6964

Ancient Greece

Cubit -
Stadium

1-4764

'4921
196-85

Ancient Rome

Stadium

201-29

-1143

APPENDIX B.

SO
y 'S

il
°i

£ S

g I
« I

"s §

S.I

S s

-'=23aa£2S"***SSS

^';:

-ssSisass^asKBissss

5; = ««

-SaS?35SJ"S3SS3S-S

S22S3

-ssssssass-'asRsss

SSffiE

-3tS«S3SSSS!35«9EI

«a"S

I : : I : < . = J = : ! I I :« ^ ^ ,

8ssss8aa2""2'-"»^a='2"

I I l^gsseggagaa-'-- '

I = = = ' = ■■ "I = ■ = ' = 'I =1 =
asass*"-*"t:asass*|sss

«sss*''"-»-sssssas*'

196

APPENDIX p.

APPENMX C.

BLOCKADE OF METZ.

The blockade of Metz by the Germans in 1S70 o£Per8 a good example of the
tactical employment of field fortification. The following notes regarding a
portion of the investment line are therefore given. The portion chosen is the
eastern sector.

This may be reckoned as extending from the Bouzonville to the Strasbourg
Road. The line of investment here, from Failly tq Mercy, is about 5 miles
long, or about ^th of the entire circuit.

The occupation of this may be divided into two periods :—

The first month (20th August — 16th September), during which it was guarded
by the 1st Corps only.^ (At this time the Germans were chiefly apprehensive
of an attempt to break out westward.)

The last six weeks, during which the 7th Corps — ^at first one division only,
but latterly the whole Corps — relieved the 1st Corps alonff the southern part
of the line. (It was " in this direction that an attempt to break out had most
chance of success, "f and had now become most probable ; also provisions
were running short in Metz, and attempts were made by the French upon the
German dep6t at Courcelles.)

The allowance of troops gradually increased, therefore, from 5,000 to 10,000
men per mile.

In the middle of October the two corps, each holding 2i miles of the
fighting position, were distributed as follows : —

The two divisions of the 1st Corps were side by side. Of the two divisions
of the 7th Corps, one was in reser^^e; they changed places every eight days.

In front line.

In rear, upwards of

1 mile.

2 miles.

4 miles-t

1st Corps.

1st Division
2nd „
Reserve Artillery

Battns. Guns.
9
3

Battns. Guns.
3 24
6 12

Battns. Guns.

3 12
36

Battns. Guns.
1

7Tn Corps.

1st Division
2nd „
Reserve Artillery

10 G

2 18
1

3 18

9 6
36

Total -

22 6

12 54

6 66

10 42

50 battalions and 1G8 guns ( 28 batterif^s).

The fighting position finally decided on for the troops on this side was about
2i miles from thp French forts; embracing Failly, Servigny, NoisseviUe,
Montoy, Ars-Laquenexy, and the woods south of Mercy-le-Haut.

The ovipost line was about 1 mile in front of this, running ftom, Villers
rOrme, east of Nouilly and Lauvallier, through CoJombey and La Grange aux
Bois to Mercy-le-Haut.

There was also a retreat position about 1 mile behind the fighting position,
ftrom St. !Parbe by Chateau Gras and Flanville, and west of Ogy and
Laquenexy.

To intrench these positions each corps had 3 companies of field pioneers
(200 strong), and these were assisted by infantry working parties.

♦ Leaving put of account a- temporary reinforcement from the 3rd to the 10th

September.

. t Goetze. % Scil. 4 to 6 miles.

APPENDIX 0, 197

26th-30tk August, — ^The pioneers of the Ist Corps (then in sole occupation) —
(a.) For the outposts —

Fortified the border of the park at Colombey with shelter trenches

and abatis.
Made shelter trenches at La Grange aux Bois and in front of

Ars-Laquenexy.
Prepared ihe Chateau of Mercy for defence, and made shelter
trenches and abatis near it.
(b.) For the main body —

They fortified Failly, Poixe, Servigny, Noisseville, and La Brasserie,
making shelter trenches and epauhnents in the intervals between
them, barring the ravine north of Noisseville with abatis, and
clearing the foreground for fire.
They prepared a retreat position in front of St. Barbe.
They also threw up shelter trenches N.W. of Laquenexy, and put
the Champel farm in a state of defence.
September lst-\6th. — After the sortie of the 31st August had shown the
insufficient strength of the position —

Shelter trenches Were thrown up behind Servigny and La Brasserie, epaul-
ments made for guns to sweep the Noisseville ra^dne, the defences of
those villages improved, and fougasses placed in front of them.
Montoy, Coincy, and the space between them were fortified.
Also the Chateau d'Aubigny and Ars-Laquenexy, and the large wood to the

south-east of Ars-Laquenexy.
September 17fA-30/A.— One division of the 7th Corps relie\'ed the 1st Corps
upon the Courcelles Road.
The defences of Ars-Laquenexy were improved, and the fighting position,
which had hitherto been further back, was brought forward to this, so as
better to secure Courcelles. The Chateau of Ars-Laquenexy was made
more defensible, and shelter trenches and epaulments thrown up to the
norfJi of it.
October \st-27th, — The 7th Corps held as far as the Saarlouis Road.
A half-sunken earthwork (150 metres of crest) ^vas made on the north-west

of Poixe.
A work of 3 faces (200 metres of crest) was begun on the Saarlouis Road a

mile behind La Brasserie; but was not finished owing to the weather.
Two works (each 150 metres of crest) were thrown up, one north of Coincy
Wood, and one east of Chateau d'Aubigny. Their parapet was to be
12^ thick, and from 6' 6" to 8' high. Their ditches, W deep, to be
palisaded and flanked by caponiers. They were to have barbettes for
6 guns and abundant blindages. Begun on the 8th October with
working parties of 400 to 500 men and a company of pioneers each, they
were s^l unfinished, though defensible, on the 28th, when the place
surrendered.
A work was also thrown up (by the 8th Corps) east of Mercy-le Haut. This

was only finished on the 28th.
Besides these works, the defensive organization of the Chateau d'Aubigny
and Ars-Laquenexy was improved ; three batteries were made at Coincy ;
Flanville was made more defensible, and a battery made there.
The troops suffered much inconvenience from the nearness of their positions
to the French forts. It was often proposed to retire them, and if the French
artillery fire had been vigorous this would have been necessary, at all events on
the northern part.

Sortie of 31st August. (Very fully described in " The Operations of the
1st Army.")

The French intention to attack was obvious early in the morning. While
other Corps were set in motion to reinforce it, the 1st Corps was concentrated
to receive the attack north of the Saarbruck Road, one brigade only being
left to guard the line to the south of this.
The French 3rd Corps was to operate between Grigy and Nouilly.

„ 4th „ „ „ May, Villers TOrme, and

Grimont.
„ 6th „ „ on the Bouzonville Road.

„ 2nd „ in reserve in the Vallieres Valley.

„ Guard ,, behind the Bois de Grimont.

198 APPENDIX D.

The attack did not begin till 4 o'clock p.m.

At 5.30 the battalion holding Noisseville and La Brasserie was driven out.

At 9 Noisseville was retaken bj the Prussians.

At 10 the French advancing along the Saarbruck Road, which was only
watched by cavahry, carried FliAnville, La Brasserie, Noisseville, and half of
Servigny.

Next morning, reinforcements having come up, the Germans recovered the
whole of Servigny, and at the third assault retook Noisseville.

APPENDIX D.

Assault of the Duppel Position.

The successful assault of the Danish works at Diippel (F.F., PI. XLIII.), by
the Prussians in 1864, afifords a good example of the conduct of such an
operation.

The works have been already noticed (par. 189). The Prussians finding
them too strong for immediate and open assault, constructed siege batteries
and approaches against them, and finally made a third parallel at about
300 ya^s from them. It was decided to deliver the assault from this parallel
on the 18th April. The Prussians had by that time been more than two
months before the position ; and for more than a month the works had been
under the fire of the siege batteries and had su£Pered greatly, especially from
the Broackerland batteries on the south side of the Wenningbund, which
enfiladed the line.

The following were the orders issued for the assault by Prince Frederic
Charles, the commander-in-chief : —

" Redoubts Nos. 1 to 6 will be simultaneously assaulted by six columns,
each bearing the number of the work it has to capture. Columns Nb«. 2 and 4
will be stronger than the others. Columns Nos. I, 3, 5, and 6 will be composed
of six, No. 2 of ten, and No. 4 of twelve companies. A company of pioneers
will be attached to Nos. 2, 4, and 6 ; a half company only to Nos. 1, 3, and 5.
The companies will be formed in columns of sections. The troops will
parade in forage caps, without knapsacks, with greatcoats slung over the
shoulder.

** In front of each column there will be a company of infantry to act as
skirmishers ; next to them will come the working party \vith rifles slung from
the shoulder. This detachment will consist of 10 pioneers provided with
spades, picks, axes, bars, &c., and with bags containing 30 lbs. of powder, and
of a company of infantry carrying planks, ladders, bags of hay, &c. The men
must take care to have the intervids necessary for them to move freely with
the things they carry. 100 paces in rear will be the storming column
proper, which will consist for Nos. 1, 3, 5, and 6 of two, for No. 2 of four, and
for No. 4 of five companies of infantry. The reserve, equal in strength to the
storming column, will follow 150 paces behind it. To each column will be
attached an officer, 4 non-commissioned officers, and 20 gunners, who will be
with the reserves. They will be provided with five resin torches per column.

" Behind the reserve of column No. 5 there will be an artillery officer and a
half-company of pioneers provided with spades, axes, picks, bars, ^c. These
men will be charged with the destruction of the barricades across the high
road between forts IV. and V., and with the repair of the road so as to allow
carriages to pass. The six columns will consist therefore : —

" Nos. 1, 3, 6, and 6 of 24 companies infantry, 2J companies pioneers.
M 2, of 10 „ „ 1 „

n 4, 01 U „ „ 1 „ „

For the barricade

j> j> a » 99

99 99 ^ J> 99

Making

Total- - 46

"IH battalions of infiintry.

5 companies of pioneers.

6 artillery detachments. (7 officers, 24 non^
commissioned officers, and 120 men.)

--<

APPENDIX D. 199

" The central reserve will consist of two brigades of infantry and four
batteries of field artillery.

" At an hour which will be notified later, the columns will be formed up on
the BiifFel-Koppel, and will be conducted thence by the engineer officers into
the second paiallel, which they should reach before daybreak. The various
tools, got ready beforehand, will there be distributed to the men of the working
parties ; each man will also receive an empty sandbag. The columns will
thfen pass on to the third parallel, and draw up in order. There will not be
room there for the reserves, so they will remain in the second paralle], and
move out of it as soon as the head of the column issues from the third parallel.
When they are in their places in the parallels, the men will fill their sandbags,
and will place their tools ready to hand against the reverse of the parapet of
the trenches.

" TJie brigades von Canstein and von Raven will form the central reserve,
and will occupy the parallels and the village of Diippel as soon as the action
begins. The four field batteries will be posted before daybreak on the high
road near the Spitzberg. The siege batteries will keep up a sustained and
't'igorous fire against the forts to be attacked for at least six hours previous to
the assault.

" At the appointed signal the six columns will simultaneously issue from the
parallel by the steps formed In its parapet ; columns Nos. 5 and 6 will oblique
at once to their left towards redoubts V. and VI., and the half company of
pioneers will make its way towards the barricades across the Sonderburg road.
As soon as the leading company of each column is out of the parallel it will
deploy into skirmishers, while advancing rapidly upon the redoubt assigned to
it, and without concerning itself in the least about maintaining connexion
with the neighbouring columns. ITie engineer officers will give the direction,
as head of the column. If the skirmishers are sto])ped by obstacles which they
cannot cross these will be levelled by the workmen who follow close upon
them, and who have been taught and practised in this work beforehand.

" Wl^B they reach the foot of the redoubts, the skirmishers must try to
surrouna them making their way by any practicable passages. They should be
told to fire at anything that shows itself above the crest of the parapet. As
soon as the working parties have opened the way, the storming column will throw
itself into the ditch, and spread right and left to mount the exterior slope of,
the parapet, directly the palisades in the bottom of the ditch shall have been
broken through. When ,the column has reached the top of the slope, the
skirmishers should be collected at the gorge of the work to cut o£P the retreat
of the garrison.

*' The blockhouses which our fire may not already have demolished will be
brought down by the pioneers, with the help of powder bags, as soon as the
garrison has been driven out of them, or bags of hay will be pushed into the
loopholes and lighted by the torches to compel the occupants to come out of
them. Each of the storming columns Nos. 2 and 4, consisting of four and
five companies respectively, will detach one company to the right and one to
the left against the retretichments made behind those works. Each of these
companies will be followed by another from the reserve.

" Tlie columns must avoid any engagement with the enemy's troops who
may issue by the intervals between the redoubts, and must devote themselves
to reaching the object assigned to them as quickly as possible. If the enemy's
troops should happen to come out they will be repulsed by the central reserve,
whid^ with this view, is placed under the orders of the general in command.

" AB soon as the columns cross the parapets of the trenches, the right wing
of the central reserve will follow the movement up to the third parallel. The
four field batteries will advance correspondingly on the high road. Imme-
diately after the capture of one or more of the forts the general in command
will jlecide on the measures to be taken, and whether the success should be
pushed further. In any case the trooj)s who have succeeded in taking a fort
must not abandon it ; they must hold it to the last man.

''The Broackerland batteries will continue their fire during the assault
against the enemy's columns that are held in reserve and against the
retrenchment made in rear of the left wing of the position."*

♦ Girard : Traite des Applications tactiques de la Fortification. Paris, 1874.

"I*

200

APPENt)l3C D.

llie commanders of the storming columns received also a confidential
order : —

" In case the troops after having crossed the ditch and mounted the interier
slope should meet mth no resistance they will at once come down again and
keep under shelter of the parapet. A non-commissioned officer of pioneers
with two men will then make his way into the work to ascertain whether there
are any traces of powder hose or mine work in the interior of the blockhq^se
or the fort." .

The assault was made at 10 a.m., that hour being chosen in order that the
Prussian artillery might have several hours of daylight beforehand, to destroy
the repairs of the previous night, and to drive Under cover the trbops and
ffuns tnat were always held ready against an assault at daybreak. Deceived
by this arrangement and expecting no assault that day, the Danish troops had
been for the most part withdrawn from the redoubts for better shelMv, and
their reserves had been* retired. In some cases the storming columns were
inside the redoubts before their own garrisons could return; and in 20
minutes Nos. 1 to 6 were all taken, with slight loss. By noon the Danes who
had had eight battalions in front line and eight in reserve were driven back
into the bridge-head opposite Sonderburg with a loss of nearly 5,000 men.
The Prussians did not venture to assault the bridge-head, and in tne afternoon
the Danes withdrew from it across the Alsen Sund, and broke up their
bridges.

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